How this calculator works
Known days supply covers the start date as day one; the first date without supply is start plus that many days. Quantity mode counts complete doses only, assumes the first dose at the start of the date, and spaces later doses evenly. The first unavailable dose date uses the whole-day offset. As-needed use, weekday-specific schedules, changed directions and early-refill rules need separate review. The result is an estimate for information only and is not medical advice.
Formula
Known supply: next date = start + days supply; last covered date = start + days supply - 1. Complete doses = floor(quantity/amount per dose). Duration = complete doses/daily frequency. Required quantity = ceil(target days x frequency) x amount per dose.
Worked example
A 30-day supply starting 1 January covers through 30 January, with the next supply needed on 31 January. Sixty tablets taken one tablet twice daily contain 60 doses, lasting 30 days under the fixed schedule.
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Frequently asked questions
Is this the earliest date the pharmacy will refill?
No. Eligibility depends on the prescription, pharmacy, insurer and local requirements. This is only a projected supply calculation.
Can I use a remaining count?
Yes. Enter the date of counting and remaining supply, with the fixed usage instructions.
How are weekly frequencies handled?
They are evenly spaced arithmetic rates. Actual weekday schedules can give a different date and are not modelled here.