Days Supply Calculation Practice
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Days supply is how long a dispensed quantity lasts, which is what insurance billing and refill timing are calculated from. Eye and ear drops, tablet and capsule counts, and metered-dose inhalers are the high-yield cases, each converting a total quantity into a per-day usage.
Formulasdays = total quantity (drops, tablets, or puffs) ÷ amount used per dayeye drops assume 20 drops/mL • always round DOWN
Worked exampleA 5 mL eye drop bottle (20 drops/mL = 100 drops), 1 drop in each eye twice daily = 4 drops/day. 100 ÷ 4 = 25 days.
Round down. You can't bill for a partial day. Inhalers count total actuations (puffs), not mL.
10 Days Supply Calculation practice problems with worked solutions
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Problem 1: Days Supply
An ophthalmic solution comes in a 10 mL bottle (assume 20 drops/mL). Sig: 1 drop in the left eye (OS) four times daily (QID). Assume the bottle is used until empty. What is the days supply? Round down to the nearest whole number.
Answer 50 days
Solution- Total drops: 10 mL × 20 drops/mL = 200 drops.
- Per day: 1 drop/dose × 4 doses/day = 4 drops/day.
- 200 drops ÷ 4 drops/day = 50 → round down = 50 days.
- Rounded as the question asks: 50 days.
Drops are the classic days-supply case: total volume × drops/mL, ÷ daily drops, rounded down. In practice most opened ophthalmics carry a 28-day discard-after-opening limit, so a very long calculated supply is capped at the bedside even when the arithmetic says otherwise.
Problem 2: Days Supply
A 237 mL bottle of acetaminophen 160 mg/5 mL suspension is dispensed. Sig: 10 mL by mouth four times daily (QID). What is the days supply? Round down to the nearest whole number.
Answer 5 days
Solution- Volume per day: 10 mL/dose × 4 doses/day = 40 mL/day.
- Days supply: 237 mL ÷ 40 mL/day ≈ 5.92 → round down = 5 days.
- Rounded as the question asks: 5 days.
For liquids, work in mL. The mg/5 mL strength is not needed unless the sig is written in mg. Always divide the dispensed volume by the daily volume, then round down.
Problem 3: Days Supply
An ophthalmic solution comes in a 2.5 mL bottle (assume 20 drops/mL). Sig: 1 drop in the left eye (OS) three times daily (TID). Assume the bottle is used until empty. What is the days supply? Round down to the nearest whole number.
Answer 16 days
Solution- Total drops: 2.5 mL × 20 drops/mL = 50 drops.
- Per day: 1 drop/dose × 3 doses/day = 3 drops/day.
- 50 drops ÷ 3 drops/day ≈ 16.67 → round down = 16 days.
- Rounded as the question asks: 16 days.
Drops are the classic days-supply case: total volume × drops/mL, ÷ daily drops, rounded down. In practice most opened ophthalmics carry a 28-day discard-after-opening limit, so a very long calculated supply is capped at the bedside even when the arithmetic says otherwise.
Problem 4: Days Supply
A 120 mL bottle of prednisolone 15 mg/5 mL solution is dispensed. Sig: 15 mL by mouth twice daily (BID). What is the days supply? Round down to the nearest whole number.
Answer 4 days
Solution- Volume per day: 15 mL/dose × 2 doses/day = 30 mL/day.
- Days supply: 120 mL ÷ 30 mL/day = 4 → round down = 4 days.
- Rounded as the question asks: 4 days.
For liquids, work in mL. The mg/5 mL strength is not needed unless the sig is written in mg. Always divide the dispensed volume by the daily volume, then round down.
Problem 5: Days Supply
A prescription for 180 tablets of metformin 500 mg is written to take 1 tablet twice daily (BID). What is the days supply? Round down to the nearest whole number.
Answer 90 days
Solution- Tablets per day: 1 × 2 = 2 tablets/day.
- Days supply: 180 tablets ÷ 2 tablets/day = 90 → round down = 90 days.
- Rounded as the question asks: 90 days.
The workhorse case: total quantity ÷ (amount per dose × doses per day), rounded down.
Problem 6: Days Supply
A 60 mL bottle of cefdinir 250 mg/5 mL suspension is dispensed. Sig: 5 mL by mouth once daily. What is the days supply? Round down to the nearest whole number.
Answer 12 days
Solution- Volume per day: 5 mL/dose × 1 doses/day = 5 mL/day.
- Days supply: 60 mL ÷ 5 mL/day = 12 → round down = 12 days.
- Rounded as the question asks: 12 days.
For liquids, work in mL. The mg/5 mL strength is not needed unless the sig is written in mg. Always divide the dispensed volume by the daily volume, then round down.
Problem 7: Days Supply
A 240 mL bottle of prednisolone 15 mg/5 mL solution is dispensed. Sig: 15 mL by mouth twice daily (BID). What is the days supply? Round down to the nearest whole number.
Answer 8 days
Solution- Volume per day: 15 mL/dose × 2 doses/day = 30 mL/day.
- Days supply: 240 mL ÷ 30 mL/day = 8 → round down = 8 days.
- Rounded as the question asks: 8 days.
For liquids, work in mL. The mg/5 mL strength is not needed unless the sig is written in mg. Always divide the dispensed volume by the daily volume, then round down.
Problem 8: Days Supply
A fluticasone/salmeterol HFA inhaler contains 120 actuations (puffs). The sig is 2 puffs twice daily (BID). What is the days supply? Round down to the nearest whole number.
Answer 30 days
Solution- Puffs per day: 2 puffs/dose × 2 doses/day = 4 puffs/day.
- Days supply: 120 actuations ÷ 4 actuations/day = 30 → round down = 30 days.
- Rounded as the question asks: 30 days.
Inhaler days supply uses total actuations (not mL). Rescue/PRN inhalers are billed on maximum daily puffs.
Problem 9: Days Supply
An ophthalmic solution comes in a 5 mL bottle (assume 20 drops/mL). Sig: 1 drop in the right eye (OD) three times daily (TID). Assume the bottle is used until empty. What is the days supply? Round down to the nearest whole number.
Answer 33 days
Solution- Total drops: 5 mL × 20 drops/mL = 100 drops.
- Per day: 1 drop/dose × 3 doses/day = 3 drops/day.
- 100 drops ÷ 3 drops/day ≈ 33.33 → round down = 33 days.
- Rounded as the question asks: 33 days.
Drops are the classic days-supply case: total volume × drops/mL, ÷ daily drops, rounded down. In practice most opened ophthalmics carry a 28-day discard-after-opening limit, so a very long calculated supply is capped at the bedside even when the arithmetic says otherwise.
Problem 10: Days Supply
A 100 mL bottle of amoxicillin 400 mg/5 mL suspension is dispensed. Sig: 5 mL by mouth three times daily (TID). What is the days supply? Round down to the nearest whole number.
Answer 6 days
Solution- Volume per day: 5 mL/dose × 3 doses/day = 15 mL/day.
- Days supply: 100 mL ÷ 15 mL/day ≈ 6.67 → round down = 6 days.
- Rounded as the question asks: 6 days.
For liquids, work in mL. The mg/5 mL strength is not needed unless the sig is written in mg. Always divide the dispensed volume by the daily volume, then round down.