Days Supply Calculation Practice
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Days supply determines how long a dispensed quantity lasts — essential for insurance billing and refill timing. 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 example
A 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.