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Lesson 3 of 6
Core
Lesson 3: Day Supply Calculations
Calculate days supply for every drug type you will see in real practice and on the PTCB exam — tablets, liquids, insulin, inhalers, eye drops, and topicals.
Master formula — works for every drug type
Days Supply = Total Quantity Dispensed ÷ Amount Used Per Day
The only formula you need. The challenge is knowing what counts as "quantity" and "per day" for each drug type.
Tablets & Capsules
DS = Qty ÷ (dose × freq/day)
90 tabs, 1 tab BID → 90 ÷ 2 = 45 days
Oral Liquids
DS = Total mL ÷ mL per day
150 mL, 5 mL BID → 150 ÷ 10 = 15 days
Insulin
DS = (pens × units/pen) ÷ units/day
3 pens, 300 u each, 30 u/day → 900 ÷ 30 = 30 days
Inhalers
DS = Total puffs ÷ puffs per day
200 puffs, 2 puffs BID → 200 ÷ 4 = 50 days
Eye / Ear Drops
DS = (vol × 20 drops/mL) ÷ drops/day
2.5 mL, 1 drop each eye QD → 50 ÷ 2 = 25 days
Topicals & Gels
DS = total grams ÷ grams per day
30 g, apply 1 g BID → 30 ÷ 2 = 15 days
Insulin pen sizes — memorize these
Standard U-100 pen (most) = 300 units (3 mL × 100 u/mL)
Standard vial = 1,000 units (10 mL × 100 u/mL)
Toujeo SoloStar U-300 = 450 units (1.5 mL)
Tresiba / Humalog U-200 = 600 units (3 mL × 200 u/mL)
Always find total units first, then divide by daily dose.
Standard vial = 1,000 units (10 mL × 100 u/mL)
Toujeo SoloStar U-300 = 450 units (1.5 mL)
Tresiba / Humalog U-200 = 600 units (3 mL × 200 u/mL)
Always find total units first, then divide by daily dose.
Common inhaler puff counts
Albuterol HFA (ProAir/Ventolin) = 200 puffs
Flovent HFA 44/110/220 mcg = 120 puffs
Symbicort = 120 puffs
Advair Diskus = 60 doses (not puffs)
Spiriva Respimat = 60 actuations (2 puffs = 1 dose)
PRN inhalers: always use maximum frequency for day supply.
Flovent HFA 44/110/220 mcg = 120 puffs
Symbicort = 120 puffs
Advair Diskus = 60 doses (not puffs)
Spiriva Respimat = 60 actuations (2 puffs = 1 dose)
PRN inhalers: always use maximum frequency for day supply.
Eye drop standard
1 drop = approximately 0.05 mL
Therefore: 20 drops per mL (standard used on PTCB)
"Each eye" = 2 drops per dose, not 1
Latanoprost 2.5 mL = ~50 drops total
Always round down to whole days.
Therefore: 20 drops per mL (standard used on PTCB)
"Each eye" = 2 drops per dose, not 1
Latanoprost 2.5 mL = ~50 drops total
Always round down to whole days.
Frequency quick reference
QD / QAM / QHS = 1×/day
BID = 2×/day | TID = 3×/day
QID = 4×/day | Q6H = 4×/day
Q8H = 3×/day | Q4H = 6×/day
Q12H = 2×/day | Q4-6H PRN = use Q4H (max)
BID = 2×/day | TID = 3×/day
QID = 4×/day | Q6H = 4×/day
Q8H = 3×/day | Q4H = 6×/day
Q12H = 2×/day | Q4-6H PRN = use Q4H (max)
★ PTCB exam strategy: Day supply appears in the Order Entry & Processing domain (22.5% of exam). Expect 3–5 day supply questions. The exam will give you a sig code and a quantity — your job is to translate the sig into doses per day, then divide. Insulin and inhaler day supply are the most commonly missed because students skip the step of finding total units/puffs first.
The 4 most common mistakes:
1. Forgetting to multiply pens × units/pen before dividing insulin — always find total units first
2. Counting "each eye" as 1 drop instead of 2
3. Using doses per administration instead of total doses per day
4. Rounding up instead of down — always round DOWN for day supply
1. Forgetting to multiply pens × units/pen before dividing insulin — always find total units first
2. Counting "each eye" as 1 drop instead of 2
3. Using doses per administration instead of total doses per day
4. Rounding up instead of down — always round DOWN for day supply
Six worked examples — one per drug type. These mirror the style and complexity of real PTCB exam questions. Work through each one yourself before reading the solution.
EasyRetailPTCB style
Patient at the counter picks up metformin 500 mg. Rx reads: Take 1 tablet by mouth twice daily. Quantity dispensed: 60 tablets.
How many days will 60 tablets last at 1 tab BID?
Step 1 — Translate BID → doses per day:
BID = 2 times per day → 1 tab × 2 = 2 tablets/day
Step 2 — Apply the formula:
60 tabs ÷ 2 tabs/day = 30 days
✓ Day supply: 30 days
EasyRetailPTCB style
Pediatric Rx: amoxicillin 250 mg/5 mL suspension. Sig: 5 mL by mouth twice daily. Quantity: 150 mL bottle.
How many days will 150 mL last at 5 mL BID?
Step 1 — Daily volume:
5 mL × 2 (BID) = 10 mL/day
Step 2 — Day supply:
150 mL ÷ 10 mL/day = 15 days
✓ Day supply: 15 days
MediumRetailPTCB style
Patient picks up insulin glargine (Lantus) SoloStar pens. Sig: inject 30 units subcutaneously every night at bedtime. Quantity: 1 box of 5 pens (each pen = 300 units).
How many days will 1 box of 5 pens last at 30 units nightly?
Step 1 — Find total units (critical first step):
5 pens × 300 units/pen = 1,500 units total
Step 2 — Day supply:
1,500 units ÷ 30 units/day = 50 days
✓ Day supply: 50 days
The #1 insulin trap: Dividing 5 (pens) by 30 (units/day) gives 0.17 — obviously wrong. You must calculate total units first. Every insulin day supply problem starts with: pens × units/pen.
MediumRetailPTCB style
Patient picks up albuterol HFA (ProAir MDI). Sig: inhale 2 puffs every 4–6 hours as needed for shortness of breath. Canister contains 200 puffs. Use maximum PRN frequency for day supply.
At max PRN use (Q4H = 6 times/day), what is the day supply for 1 inhaler?
Step 1 — Puffs per day at max frequency (Q4H = 6×/day):
2 puffs × 6 = 12 puffs/day
Step 2 — Day supply (round down):
200 ÷ 12 = 16.67 → 16 days
✓ Day supply: 16 days — always round down
MediumRetailPTCB style
Patient picks up latanoprost 0.005% ophthalmic solution. Sig: instill 1 drop in each eye every evening. Bottle size: 2.5 mL.
How many days will the 2.5 mL bottle last?
Step 1 — Total drops in bottle (20 drops per mL):
2.5 mL × 20 = 50 drops total
Step 2 — Drops per day ("each eye" = both eyes = 2 drops):
1 drop × 2 eyes × 1 (QHS) = 2 drops/day
Step 3 — Day supply:
50 drops ÷ 2 drops/day = 25 days
✓ Day supply: 25 days
"Each eye" means 2: Every time you see "each eye" or "both eyes," multiply drops per dose by 2. Entering 1 drop per day instead of 2 doubles the day supply — a common insurance audit flag.
HardPatient scenarioPTCB style
Mrs. Torres has type 2 diabetes. Rx: insulin lispro (Humalog), inject 10 units with each meal and 5 units with bedtime snack. She eats 3 meals per day. Quantity: 2 vials (1,000 units each).
How many days will 2 vials last for Mrs. Torres?
Step 1 — Mealtime units per day:
10 units × 3 meals = 30 units
Step 2 — Add bedtime dose:
30 + 5 = 35 units/day
Step 3 — Total units in 2 vials:
2 × 1,000 = 2,000 units
Step 4 — Day supply (round down):
2,000 ÷ 35 = 57.1 → 57 days
✓ Day supply: 57 days
Difficulty
Context
Easy
Retail
Tablets
Patient picks up metformin 500 mg. Sig: 1 tablet by mouth twice daily.
How many days will 60 tablets last?
Answer: 30 days
1 tab × 2 (BID) = 2 tabs/day. 60 ÷ 2 = 30 days. BID = twice per day.
1 tab × 2 (BID) = 2 tabs/day. 60 ÷ 2 = 30 days. BID = twice per day.
Easy
Retail
Tablets
Patient picks up lisinopril 10 mg. Sig: 1 tablet by mouth once daily.
A 90-tablet supply will last how many days?
Answer: 90 days
1 tab × 1 (QD) = 1 tab/day. 90 ÷ 1 = 90 days. QD = once per day.
1 tab × 1 (QD) = 1 tab/day. 90 ÷ 1 = 90 days. QD = once per day.
Easy
Retail
Tablets
10-day antibiotic course. Sig: 1 capsule by mouth three times daily.
How many capsules are needed for a complete 10-day supply?
Answer: 30 capsules
1 cap × 3 (TID) = 3 caps/day. 3 × 10 days = 30 capsules. Working backwards from days to quantity.
1 cap × 3 (TID) = 3 caps/day. 3 × 10 days = 30 capsules. Working backwards from days to quantity.
Easy
Retail
Tablets
Patient on atorvastatin 20 mg. Sig: 1 tablet by mouth at bedtime. Quantity: 30 tablets.
How many days will 30 tablets last at 1 tablet QHS?
Answer: 30 days
QHS = every bedtime = once daily = 1 tab/day. 30 ÷ 1 = 30 days. QHS, QD, and QAM all mean once per day.
QHS = every bedtime = once daily = 1 tab/day. 30 ÷ 1 = 30 days. QHS, QD, and QAM all mean once per day.
Med
Retail
Tablets
Prednisone taper pack. Sig: 3 tablets daily for 5 days, then 2 tablets daily for 5 days, then 1 tablet daily for 5 days.
How many total tablets are needed for the full taper?
Answer: 30 tablets
Phase 1: 3 × 5 = 15 tabs. Phase 2: 2 × 5 = 10 tabs. Phase 3: 1 × 5 = 5 tabs. Total: 15 + 10 + 5 = 30 tablets over 15 days.
Phase 1: 3 × 5 = 15 tabs. Phase 2: 2 × 5 = 10 tabs. Phase 3: 1 × 5 = 5 tabs. Total: 15 + 10 + 5 = 30 tablets over 15 days.
Med
Retail
Tablets
Ibuprofen 400 mg. Sig: 2 tablets by mouth every 6 hours as needed for pain. Quantity: 120 tablets.
Using maximum scheduled dosing (Q6H = 4 times/day), what is the day supply?
Answer: 15 days
2 tabs × 4 (Q6H = 4×/day) = 8 tabs/day at max. 120 ÷ 8 = 15 days. PRN medications: always use maximum daily frequency to calculate day supply.
2 tabs × 4 (Q6H = 4×/day) = 8 tabs/day at max. 120 ÷ 8 = 15 days. PRN medications: always use maximum daily frequency to calculate day supply.
Med
Retail
Tablets
Sig: Take ½ tablet daily for 2 weeks, then 1 tablet daily after that. Quantity: 60 tablets.
How many days will 60 tablets last following this titration schedule?
Answer: 67 days
Phase 1 (2 weeks = 14 days): 0.5 tab/day × 14 = 7 tabs used. Remaining: 60 − 7 = 53 tabs. Phase 2: 53 tabs ÷ 1 tab/day = 53 more days. Total: 14 + 53 = 67 days.
Phase 1 (2 weeks = 14 days): 0.5 tab/day × 14 = 7 tabs used. Remaining: 60 − 7 = 53 tabs. Phase 2: 53 tabs ÷ 1 tab/day = 53 more days. Total: 14 + 53 = 67 days.
Med
Retail
Tablets
Sig: 1 tablet every morning. Insurance approves a 90-day supply. Quantity: 90 tablets.
What day supply should be entered into the system?
Answer: 90 days
QAM = every morning = once daily = 1 tab/day. 90 ÷ 1 = 90 days.
QAM = every morning = once daily = 1 tab/day. 90 ÷ 1 = 90 days.
Hard
Hospital
Tablets
Discharge Rx. Warfarin dose varies: Monday/Wednesday/Friday take 2 tablets of 2.5 mg; all other days take 1 tablet. Dispensing 2.5 mg tablets. Patient needs a 4-week supply.
How many 2.5 mg warfarin tablets are needed for exactly 4 weeks?
Answer: 40 tablets
Per week: Mon/Wed/Fri (3 days) × 2 tabs = 6 tabs. Other 4 days × 1 tab = 4 tabs. Total per week = 6 + 4 = 10 tabs. For 4 weeks: 10 × 4 = 40 tablets.
Per week: Mon/Wed/Fri (3 days) × 2 tabs = 6 tabs. Other 4 days × 1 tab = 4 tabs. Total per week = 6 + 4 = 10 tabs. For 4 weeks: 10 × 4 = 40 tablets.
Hard
Patient scenario
Tablets
Sildenafil 50 mg. Sig: Take 1 tablet as needed approximately 1 hour before activity, no more than once daily. Patient reports using it about 3 times per week. Quantity: 30 tablets.
Based on the patient's reported use (3×/week), how many days will 30 tablets last?
Answer: 70 days
3 tablets/week ÷ 7 days/week = 3/7 tablets per day. 30 ÷ (3/7) = 30 × (7/3) = 70 days. Alternatively: 30 tablets ÷ 3 per week = 10 weeks × 7 = 70 days.
3 tablets/week ÷ 7 days/week = 3/7 tablets per day. 30 ÷ (3/7) = 30 × (7/3) = 70 days. Alternatively: 30 tablets ÷ 3 per week = 10 weeks × 7 = 70 days.
Easy
Retail
Oral liquid
Child Rx: amoxicillin 250 mg/5 mL suspension. Sig: 5 mL by mouth twice daily. Quantity: 150 mL.
What is the day supply for 150 mL at 5 mL BID?
Answer: 15 days
5 mL × 2 (BID) = 10 mL/day. 150 mL ÷ 10 mL/day = 15 days.
5 mL × 2 (BID) = 10 mL/day. 150 mL ÷ 10 mL/day = 15 days.
Easy
Retail
Oral liquid
Allergy syrup. Sig: 10 mL by mouth once daily at bedtime. Quantity: 120 mL bottle.
How many days will the 120 mL bottle last?
Answer: 12 days
10 mL × 1 (QHS) = 10 mL/day. 120 mL ÷ 10 mL/day = 12 days.
10 mL × 1 (QHS) = 10 mL/day. 120 mL ÷ 10 mL/day = 12 days.
Easy
Patient scenario
Oral liquid
Azithromycin Z-pack suspension for a child. Sig: 10 mL on Day 1, then 5 mL once daily on Days 2–5.
How many total mL are needed for the complete 5-day course?
Answer: 30 mL
Day 1: 10 mL. Days 2–5: 5 mL × 4 days = 20 mL. Total: 10 + 20 = 30 mL. A standard azithromycin 200 mg/5 mL pack is exactly 30 mL for this reason.
Day 1: 10 mL. Days 2–5: 5 mL × 4 days = 20 mL. Total: 10 + 20 = 30 mL. A standard azithromycin 200 mg/5 mL pack is exactly 30 mL for this reason.
Med
Retail
Oral liquid
Prednisolone oral solution. Patient weighs 22 kg. Prescribed dose: 1 mg/kg/day. Concentration available: 15 mg/5 mL.
How many mL should the patient receive per day?
Answer: 7.3 mL
Dose: 1 mg/kg × 22 kg = 22 mg/day. Volume: 22 mg ÷ (15 mg/5 mL) = 22 × (5/15) = 7.3 mL/day. Round to nearest tenth.
Dose: 1 mg/kg × 22 kg = 22 mg/day. Volume: 22 mg ÷ (15 mg/5 mL) = 22 × (5/15) = 7.3 mL/day. Round to nearest tenth.
Med
Retail
Oral liquid
Augmentin ES suspension. Sig: 6.4 mL by mouth twice daily for 10 days.
What total volume (mL) is needed for the complete 10-day course?
Answer: 128 mL
6.4 mL × 2 (BID) = 12.8 mL/day. 12.8 mL × 10 days = 128 mL. Pharmacies typically dispense a 150 mL bottle, but the day supply calculation is based on the prescribed dose.
6.4 mL × 2 (BID) = 12.8 mL/day. 12.8 mL × 10 days = 128 mL. Pharmacies typically dispense a 150 mL bottle, but the day supply calculation is based on the prescribed dose.
Med
Patient scenario
Oral liquid
Ms. Carter takes hydroxyzine syrup for anxiety. Sig: 5 mL three times daily as needed. She reports taking it once daily on average. Quantity: 1 pint (473 mL). The question asks what to enter based on reported use.
Based on her reported use of 5 mL once daily, what day supply should be entered?
Answer: 94 days
At reported use of 5 mL × 1 daily = 5 mL/day. 473 mL ÷ 5 mL/day = 94.6 → 94 days (round down). Real-world note: if entering for insurance, most systems use max PRN dose (15 mL/day → 31 days). This question specifies reported use, so 94 days is correct here.
At reported use of 5 mL × 1 daily = 5 mL/day. 473 mL ÷ 5 mL/day = 94.6 → 94 days (round down). Real-world note: if entering for insurance, most systems use max PRN dose (15 mL/day → 31 days). This question specifies reported use, so 94 days is correct here.
Hard
Hospital
Oral liquid
Post-op patient. Lactulose for hepatic encephalopathy. Dose: 30 mL three times daily. Patient receives one 2 L (2,000 mL) bottle.
How many days will the 2 L bottle last at 30 mL TID?
Answer: 22 days
30 mL × 3 (TID) = 90 mL/day. 2,000 mL ÷ 90 mL/day = 22.2 → 22 days (round down).
30 mL × 3 (TID) = 90 mL/day. 2,000 mL ÷ 90 mL/day = 22.2 → 22 days (round down).
Hard
Patient scenario
Oral liquid
OTP clinic patient. Methadone 5 mg/5 mL. Daily observed dose: 80 mg. Patient receives 6 take-home bottles of 100 mL each.
How many days of take-home supply do 6 × 100 mL bottles provide at 80 mg/day?
Answer: 7 days
Volume per day: 80 mg ÷ (5 mg/5 mL) = 80 mg × (5 mL/5 mg) = 80 mL/day. Total volume: 6 × 100 = 600 mL. 600 ÷ 80 = 7.5 → 7 days (round down).
Volume per day: 80 mg ÷ (5 mg/5 mL) = 80 mg × (5 mL/5 mg) = 80 mL/day. Total volume: 6 × 100 = 600 mL. 600 ÷ 80 = 7.5 → 7 days (round down).
Easy
Retail
Insulin
Sig: inject 20 units subcutaneously once daily at bedtime. Quantity: 1 SoloStar pen (300 units).
How many days will 1 pen last at 20 units/day?
Answer: 15 days
300 units ÷ 20 units/day = 15 days. Standard SoloStar pen = 300 units (3 mL × 100 u/mL).
300 units ÷ 20 units/day = 15 days. Standard SoloStar pen = 300 units (3 mL × 100 u/mL).
Easy
Retail
Insulin
Sig: inject 30 units subcutaneously every night. Quantity: 1 box of 5 SoloStar pens (300 units each).
How many days will 1 box (5 pens) last at 30 units/day?
Answer: 50 days
Total units: 5 × 300 = 1,500 units. 1,500 ÷ 30 units/day = 50 days.
Total units: 5 × 300 = 1,500 units. 1,500 ÷ 30 units/day = 50 days.
Easy
Retail
Insulin
Humulin R 100 u/mL, 10 mL vial. Sig: inject 15 units before each meal (3 meals per day).
A patient injects 15 units before each of 3 daily meals. How many days will one 10 mL vial of Humulin R (100 u/mL) last?
Answer: 22 days
Total units: 10 mL × 100 u/mL = 1,000 units. Daily: 15 × 3 = 45 units/day. 1,000 ÷ 45 = 22.2 → 22 days (round down).
Total units: 10 mL × 100 u/mL = 1,000 units. Daily: 15 × 3 = 45 units/day. 1,000 ÷ 45 = 22.2 → 22 days (round down).
Med
Retail
Insulin
Levemir FlexPen (300 units). Sig: inject 40 units twice daily.
How many days will one Levemir FlexPen last? Round down.
Answer: 3 days
Daily dose: 40 × 2 = 80 units/day. 300 ÷ 80 = 3.75 → 3 days (round down). Patients on high doses need multiple pens per fill.
Daily dose: 40 × 2 = 80 units/day. 300 ÷ 80 = 3.75 → 3 days (round down). Patients on high doses need multiple pens per fill.
Med
Retail
Insulin
Sig: inject 12 units with each meal (3 meals/day) + 8 units at bedtime. Quantity: 2 vials (1,000 units each).
How many days will 2 vials (2,000 units) last? Round down.
Answer: 45 days
Daily: (12 × 3) + 8 = 36 + 8 = 44 units/day. Total: 2,000 units. 2,000 ÷ 44 = 45.4 → 45 days.
Daily: (12 × 3) + 8 = 36 + 8 = 44 units/day. Total: 2,000 units. 2,000 ÷ 44 = 45.4 → 45 days.
Med
Patient scenario
Insulin
Mr. Patel uses 1 unit per 15g carbohydrate. He eats ~60g carbs per meal, 3 meals/day, plus 25 units of basal insulin nightly. Quantity: 3 NovoLog pens (300 units each).
How many days will 3 NovoLog pens (900 units) last?
Answer: 24 days
Mealtime: (60 ÷ 15) = 4 units/meal × 3 = 12 units/day. Basal: 25 units/day. Total: 12 + 25 = 37 units/day. 900 ÷ 37 = 24.3 → 24 days.
Mealtime: (60 ÷ 15) = 4 units/meal × 3 = 12 units/day. Basal: 25 units/day. Total: 12 + 25 = 37 units/day. 900 ÷ 37 = 24.3 → 24 days.
Med
Retail
Insulin
Humulin N 100 u/mL, 10 mL vial. Sig: 30 units every morning and 20 units every bedtime.
Patient takes 30 units AM and 20 units PM of Humulin N. How many days will one 10 mL vial provide?
Answer: 20 days
Daily: 30 (AM) + 20 (PM) = 50 units/day. Vial = 1,000 units. 1,000 ÷ 50 = 20 days.
Daily: 30 (AM) + 20 (PM) = 50 units/day. Vial = 1,000 units. 1,000 ÷ 50 = 20 days.
Hard
Hospital
Insulin
Toujeo SoloStar pen contains 300 u/mL in a 1.5 mL pen = 450 units per pen. Patient dose: 60 units nightly. Insurance approves 3 pens per fill.
How many days will 3 Toujeo pens last at 60 units/day? Round down.
Answer: 22 days
Total units: 3 × 450 = 1,350 units. 1,350 ÷ 60 = 22.5 → 22 days. Important: Toujeo pens = 450 units, not the standard 300 units. This is a common exam trap.
Total units: 3 × 450 = 1,350 units. 1,350 ÷ 60 = 22.5 → 22 days. Important: Toujeo pens = 450 units, not the standard 300 units. This is a common exam trap.
Hard
Patient scenario
Insulin
U-200 KwikPen: 200 u/mL × 3 mL = 600 units per pen. Sig: 50 units before each meal, 3 meals per day.
How many days will 2 U-200 KwikPens (1,200 units total) last? Round down.
Answer: 8 days
Total units: 2 × 600 = 1,200 units. Daily: 50 × 3 = 150 units/day. 1,200 ÷ 150 = 8 days. U-200 pens hold double the units of standard U-100 pens.
Total units: 2 × 600 = 1,200 units. Daily: 50 × 3 = 150 units/day. 1,200 ÷ 150 = 8 days. U-200 pens hold double the units of standard U-100 pens.
Hard
Retail
Insulin
Tresiba U-200 FlexTouch: 200 u/mL × 3 mL = 600 units per pen. Patient dose: 80 units nightly. Quantity: 3 pens.
How many days will 3 Tresiba pens (1,800 units) last at 80 units/day? Round down.
Answer: 22 days
Total units: 3 × 600 = 1,800 units. 1,800 ÷ 80 = 22.5 → 22 days. Tresiba U-200 = 600 units/pen. Know your insulin pen sizes cold.
Total units: 3 × 600 = 1,800 units. 1,800 ÷ 80 = 22.5 → 22 days. Tresiba U-200 = 600 units/pen. Know your insulin pen sizes cold.
Easy
Retail
Inhaler
Sig: inhale 2 puffs every 4–6 hours as needed for wheezing. 1 canister = 200 puffs. Use maximum PRN frequency for day supply.
At Q4H (max frequency = 6 times/day), what is the day supply?
Answer: 16 days
Max puffs/day: 2 × 6 = 12 puffs/day. 200 ÷ 12 = 16.67 → 16 days. Always round down. Always use max frequency for PRN inhalers.
Max puffs/day: 2 × 6 = 12 puffs/day. 200 ÷ 12 = 16.67 → 16 days. Always round down. Always use max frequency for PRN inhalers.
Easy
Retail
Inhaler
Flovent HFA 44 mcg, 120 actuations. Sig: inhale 2 puffs twice daily.
What is the day supply for 1 Flovent inhaler?
Answer: 30 days
2 puffs × 2 (BID) = 4 puffs/day. 120 ÷ 4 = 30 days.
2 puffs × 2 (BID) = 4 puffs/day. 120 ÷ 4 = 30 days.
Easy
Retail
Inhaler
Spiriva Respimat 2.5 mcg. Each dose = 2 puffs. Device has 60 actuations. Sig: inhale 2 puffs (= 1 dose) once daily.
What is the day supply for the Spiriva Respimat?
Answer: 30 days
2 puffs × 1 (QD) = 2 puffs/day. 60 ÷ 2 = 30 days. Spiriva Respimat: 60 actuations = 30 doses.
2 puffs × 1 (QD) = 2 puffs/day. 60 ÷ 2 = 30 days. Spiriva Respimat: 60 actuations = 30 doses.
Med
Retail
Inhaler
Symbicort 160/4.5 mcg, 120 puffs per inhaler. Sig: inhale 2 puffs twice daily. Patient picks up 3 inhalers.
What is the total day supply for all 3 inhalers?
Answer: 90 days
Per inhaler: 2 × 2 (BID) = 4 puffs/day. 120 ÷ 4 = 30 days per inhaler. 3 inhalers × 30 = 90 days.
Per inhaler: 2 × 2 (BID) = 4 puffs/day. 120 ÷ 4 = 30 days per inhaler. 3 inhalers × 30 = 90 days.
Med
Retail
Inhaler
Advair Diskus 250/50, 60 doses. Sig: inhale 1 dose (blister) twice daily. Note: each blister = 1 dose, not counted in puffs.
What is the day supply for Advair Diskus at 1 dose BID?
Answer: 30 days
1 dose × 2 (BID) = 2 doses/day. 60 doses ÷ 2 = 30 days. Advair Diskus counts doses (blisters), not individual puffs.
1 dose × 2 (BID) = 2 doses/day. 60 doses ÷ 2 = 30 days. Advair Diskus counts doses (blisters), not individual puffs.
Med
Patient scenario
Inhaler
COPD patient. Combivent Respimat, 120 actuations. Sig: inhale 1 puff four times daily.
How many days will 120 actuations last at 1 puff QID?
Answer: 30 days
1 puff × 4 (QID) = 4 puffs/day. 120 ÷ 4 = 30 days. QID = four times per day.
1 puff × 4 (QID) = 4 puffs/day. 120 ÷ 4 = 30 days. QID = four times per day.
Hard
Hospital
Inhaler
Perforomist 20 mcg/2 mL nebulizer solution. Box of 60 unit-dose vials. Sig: inhale contents of 1 vial via nebulizer twice daily.
How many days will one box of 60 vials last?
Answer: 30 days
1 vial × 2 (BID) = 2 vials/day. 60 ÷ 2 = 30 days. Nebulizer solutions count by unit-dose vials.
1 vial × 2 (BID) = 2 vials/day. 60 ÷ 2 = 30 days. Nebulizer solutions count by unit-dose vials.
Hard
Patient scenario
Inhaler
Patient fills both: Albuterol (200 puffs, 2 puffs Q4–6H PRN) and Flovent 110 mcg (120 puffs, 2 puffs BID). Both filled same day.
Which inhaler has the longer day supply? (Use Q4H max for albuterol.)
Answer: Flovent — 30 days vs 16 days for albuterol
Albuterol at max Q4H: 2 × 6 = 12/day → 200 ÷ 12 = 16 days. Flovent: 2 × 2 = 4/day → 120 ÷ 4 = 30 days. Flovent lasts longer at 30 days. This explains why rescue and controller inhalers get out of sync.
Albuterol at max Q4H: 2 × 6 = 12/day → 200 ÷ 12 = 16 days. Flovent: 2 × 2 = 4/day → 120 ÷ 4 = 30 days. Flovent lasts longer at 30 days. This explains why rescue and controller inhalers get out of sync.
Med
Retail
Eye/ear drops
Sig: instill 1 drop in each eye every evening. Bottle: 2.5 mL. Standard: 20 drops per mL.
How many days will the 2.5 mL bottle last?
Answer: 25 days
Total drops: 2.5 × 20 = 50 drops. Drops/day: 1 × 2 eyes = 2 drops/day. 50 ÷ 2 = 25 days.
Total drops: 2.5 × 20 = 50 drops. Drops/day: 1 × 2 eyes = 2 drops/day. 50 ÷ 2 = 25 days.
Med
Retail
Eye/ear drops
Sig: instill 1 drop in the LEFT eye only, twice daily. Bottle: 5 mL.
How many days will the 5 mL bottle last?
Answer: 50 days
Total drops: 5 × 20 = 100 drops. Left eye only: 1 drop × 2 (BID) = 2 drops/day. 100 ÷ 2 = 50 days. Key: only the left eye — not both.
Total drops: 5 × 20 = 100 drops. Left eye only: 1 drop × 2 (BID) = 2 drops/day. 100 ÷ 2 = 50 days. Key: only the left eye — not both.
Hard
Retail
Eye/ear drops
Post-operative. Sig: instill 1–2 drops in right eye every 4–6 hours. Use 2 drops at maximum frequency (Q4H) for day supply.
How many days will 5 mL last using 2 drops 6 times/day in one eye? Round down.
Answer: 8 days
Total drops: 5 × 20 = 100 drops. Max use: 2 drops × 6 = 12 drops/day. 100 ÷ 12 = 8.3 → 8 days.
Total drops: 5 × 20 = 100 drops. Max use: 2 drops × 6 = 12 drops/day. 100 ÷ 12 = 8.3 → 8 days.
Hard
Hospital
Eye/ear drops
Sig: instill 4 drops in the affected ear 3 times daily for 7 days. Bottle: 10 mL.
How many mL are used for the full 7-day course? Does 1 bottle (10 mL) cover the full course?
Answer: 4.2 mL used — 1 bottle is more than enough
Drops/day: 4 × 3 = 12 drops/day. Over 7 days: 12 × 7 = 84 drops. Volume: 84 ÷ 20 drops/mL = 4.2 mL. One 10 mL bottle is more than enough. Enter 7 days.
Drops/day: 4 × 3 = 12 drops/day. Over 7 days: 12 × 7 = 84 drops. Volume: 84 ÷ 20 drops/mL = 4.2 mL. One 10 mL bottle is more than enough. Enter 7 days.
Easy
Retail
Topical
Sig: apply a thin layer to the affected area twice daily. Estimated use: 0.5 g per application. Quantity: 30 g tube.
How many days will the 30 g tube last?
Answer: 30 days
0.5 g × 2 (BID) = 1 g/day. 30 g ÷ 1 g/day = 30 days.
0.5 g × 2 (BID) = 1 g/day. 30 g ÷ 1 g/day = 30 days.
Med
Retail
Topical
Sig: insert 5 g intravaginally once daily at bedtime for 5 days. Tube: 70 g.
What day supply should be entered for the 70 g tube at 5 g/day?
Answer: 14 days
5 g × 1 (QHS) = 5 g/day. 70 g ÷ 5 g/day = 14. Enter 14 days as the calculated day supply, even though the course is only 5 days. Pharmacies enter day supply based on quantity dispensed ÷ daily use.
5 g × 1 (QHS) = 5 g/day. 70 g ÷ 5 g/day = 14. Enter 14 days as the calculated day supply, even though the course is only 5 days. Pharmacies enter day supply based on quantity dispensed ÷ daily use.
Med
Patient scenario
Topical
Androgel 1%. Sig: apply contents of 2 packets topically once daily. Each packet = 5 g. Box contains 30 packets.
A box of 30 packets will last how many days?
Answer: 15 days
2 packets × 1 (QD) = 2 packets/day. 30 ÷ 2 = 15 days. Count packets per day, not grams, when packets are the dispensed unit.
2 packets × 1 (QD) = 2 packets/day. 30 ÷ 2 = 15 days. Count packets per day, not grams, when packets are the dispensed unit.
Hard
Hospital
Topical
Atopic dermatitis. Sig: apply thin layer to trunk and arms twice daily. Estimated use: 2 g per application. Quantity: 60 g.
How many days will 60 g last at 2 g per application, BID?
Answer: 15 days
2 g × 2 (BID) = 4 g/day. 60 g ÷ 4 g/day = 15 days.
2 g × 2 (BID) = 4 g/day. 60 g ÷ 4 g/day = 15 days.
Med
Retail
Multi-step
Patient drops off 3 Rxs: (1) Lisinopril 10 mg #90, 1 QD. (2) Metformin 500 mg #180, 1 BID. (3) Atorvastatin 40 mg #90, 1 QD.
Which Rx will run out first?
Answer: All three run out at the same time
Lisinopril: 90 ÷ 1 = 90 days. Metformin: 180 ÷ 2 = 90 days. Atorvastatin: 90 ÷ 1 = 90 days. All three are 90-day supplies. This is a medication synchronization (med sync) fill — aligned intentionally.
Lisinopril: 90 ÷ 1 = 90 days. Metformin: 180 ÷ 2 = 90 days. Atorvastatin: 90 ÷ 1 = 90 days. All three are 90-day supplies. This is a medication synchronization (med sync) fill — aligned intentionally.
Med
Retail
Multi-step
Patient fills 30 sertraline tablets (1 QD = 30-day supply) on Day 1. She calls on Day 25 requesting a refill. The pharmacy policy allows refill once 75% of the supply is used.
On Day 25, can the patient refill her sertraline?
Answer: Yes — 75% threshold was reached before Day 25
75% of 30 days = 22.5 days. Rounded up: earliest refill is Day 23. She is calling on Day 25, which is after Day 23. Yes, she can refill. By Day 25 she has used 25 out of 30 doses (83%), which exceeds the 75% threshold.
75% of 30 days = 22.5 days. Rounded up: earliest refill is Day 23. She is calling on Day 25, which is after Day 23. Yes, she can refill. By Day 25 she has used 25 out of 30 doses (83%), which exceeds the 75% threshold.
Med
Patient scenario
Multi-step
Rx: Adderall XR 20 mg, 2 capsules daily. Qty: 60 capsules. Schedule II — most states limit to 30-day supply.
How many days does Qty #60 represent, and is it within the CII limit?
Answer: 30 days — yes, within the 30-day limit
60 caps ÷ 2 caps/day = 30 days exactly. This is within the typical CII 30-day limit. If the Rx were for #90 (45 days), it would require clarification or a new Rx.
60 caps ÷ 2 caps/day = 30 days exactly. This is within the typical CII 30-day limit. If the Rx were for #90 (45 days), it would require clarification or a new Rx.
Hard
Hospital
Multi-step
DVT prophylaxis post-discharge. Sig: inject 40 mg subcutaneously once daily. Patient needs 10 days of outpatient therapy. Syringes come in cartons of 10.
How many cartons (10 syringes each) are needed for 10 days?
Answer: 1 carton — exactly enough
1 syringe/day × 10 days = 10 syringes. 1 carton = 10 syringes. Exactly 1 carton. Know standard carton sizes for common injectables.
1 syringe/day × 10 days = 10 syringes. 1 carton = 10 syringes. Exactly 1 carton. Know standard carton sizes for common injectables.
Hard
Retail
Multi-step
Type 2 diabetes patient. Rx 1: Metformin 1000 mg #180 tabs, 1 BID. Rx 2: Insulin glargine 10 units nightly, 5 pens (300 units each).
Which medication runs out first and when?
Answer: Metformin at 90 days — runs out first
Metformin: 180 ÷ (1×2) = 90 days. Insulin: 5 × 300 = 1,500 units ÷ 10 units/day = 150 days. Metformin runs out first at 90 days. The patient needs to refill metformin before insulin.
Metformin: 180 ÷ (1×2) = 90 days. Insulin: 5 × 300 = 1,500 units ÷ 10 units/day = 150 days. Metformin runs out first at 90 days. The patient needs to refill metformin before insulin.
Hard
Retail
Multi-step
Insurance requires exactly a 90-day supply. Patient uses 50 units of insulin glargine nightly. SoloStar pens are 300 units each.
How many pens are needed to cover exactly 90 days? (Round up — patient must not run short.)
Answer: 15 pens
Units needed: 50 × 90 = 4,500 units. Pens: 4,500 ÷ 300 = 15 pens exactly. When calculating pens to dispense, round up if not a whole number so the patient has enough. Here it divides evenly.
Units needed: 50 × 90 = 4,500 units. Pens: 4,500 ÷ 300 = 15 pens exactly. When calculating pens to dispense, round up if not a whole number so the patient has enough. Here it divides evenly.
Hard
Retail
Multi-step
Vivitrol 380 mg IM injection. Given once every 4 weeks. Patient picks up 1 injection kit.
What day supply should be entered for 1 Vivitrol injection?
Answer: 28 days
Once every 4 weeks = every 28 days. Enter 28 days, not 30. The manufacturer specifies 4 weeks (4 × 7 = 28), not every calendar month.
Once every 4 weeks = every 28 days. Enter 28 days, not 30. The manufacturer specifies 4 weeks (4 × 7 = 28), not every calendar month.
Hard
Hospital
Multi-step
Home infusion: vancomycin 1,500 mg in 250 mL NS, infuse once daily. Specialty pharmacy dispenses 7 bags.
What day supply should be entered for these 7 vancomycin IV bags?
Answer: 7 days
1 bag per day × 7 bags = 7 days. IV bags for home infusion are entered as 1 day per bag when the sig is once daily.
1 bag per day × 7 bags = 7 days. IV bags for home infusion are entered as 1 day per bag when the sig is once daily.
Hard
Patient scenario
Multi-step
Oxycodone 5 mg. Sig: take 1–2 tablets every 4–6 hours as needed for pain. Qty: 60 tablets. For CII, use maximum dosing for day supply.
What day supply should be entered using maximum dosing (2 tabs Q4H)?
Answer: 5 days
Maximum: 2 tabs × 6 (Q4H) = 12 tabs/day. 60 ÷ 12 = 5 days. CII controlled substances use maximum dosing for day supply entry. This flags appropriately in PMP systems.
Maximum: 2 tabs × 6 (Q4H) = 12 tabs/day. 60 ÷ 12 = 5 days. CII controlled substances use maximum dosing for day supply entry. This flags appropriately in PMP systems.
Hard
Retail
Multi-step
Medrol Dosepak (methylprednisolone 4 mg). Fixed taper: Day 1: 6 tabs, Day 2: 5 tabs, Day 3: 4 tabs, Day 4: 3 tabs, Day 5: 2 tabs, Day 6: 1 tab.
How many total tablets are in the Medrol Dosepak, and what is the day supply?
Answer: 21 tablets — 6 days
6+5+4+3+2+1 = 21 tablets, taken over 6 days. The Medrol Dosepak is a pre-packaged fixed taper. Memorize: 21 tablets, 6 days. Very common retail dispensing scenario.
6+5+4+3+2+1 = 21 tablets, taken over 6 days. The Medrol Dosepak is a pre-packaged fixed taper. Memorize: 21 tablets, 6 days. Very common retail dispensing scenario.
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Lesson 3 · Day Supply Calculations · AlabamaPharmTech.com
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