How to use this calculator
- Enter or choose quantity dispensed.
- Enter or choose units per dose.
- Enter or choose doses per day.
- The days supply updates as you type. Use Copy result or Share to keep it.
Method
Days supply = Quantity dispensed ÷ (Units per dose × Doses per day)
- Quantity dispensed
- total units supplied
- Units per dose
- tablets, mL, drops or puffs taken each time
- Doses per day
- how many times a day, from the directions
Worked example
- A 2.5 mL bottle at 20 drops/mL holds 50 drops; one drop in each eye is 2 drops per dose.
- Daily use = 2 drops × 2 times = 4 drops.
- Days supply = 50 ÷ 4 = 12.5 days (12 full days, 2 drops left).
A 50-drop bottle used one drop in each eye twice a day lasts 12.5 days, the figure in CMS’s pharmacy billing job aid.
What the result means
Use the result for billing and refill planning. Products dosed on a cycle (weekly patches, rings with a break week) need the cycle length, not a simple count: CMS bills four weekly patches as 28 days.
Assumptions and limits
- The patient follows the directions exactly, every day.
- The quantity and the dose use the same unit.
- “As needed” directions, tapering doses and cyclical products need manual calculation.
- Drops per mL vary between products; use the manufacturer’s figure.
Questions
How do I work out days supply for an inhaler?
Divide the actuations in the inhaler by the puffs used per day. A 120-dose inhaler at 4 puffs a day is a 30-day supply.
Should I round days supply up or down?
Follow your payer’s rules. Many systems take the whole number of days the supply fully covers.
Sources
Please note: This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health.