Refill Due Date Calculator

Work out refill due date instantly with clear inputs, formula shown and shareable results.

About Refill Due Date Calculator

Counts forward from the dispensing date to the run-out date and sets a reminder date the chosen number of days earlier.

Formula

Refill timing

Run-out date = date dispensed + days supply; refill date = run-out date - reminder lead time

Worked example

With the default values below, Refill Due Date Calculator returns Order the refill by of September 26, 2026. Change any input above and every figure here is recalculated in your browser.

Inputs used

Date dispensed: 2026-09-01
Days supplyaccepts 1–365: 30
Remind this many days earlyaccepts 0–30: 5

Results

Order the refill by: September 26, 2026
Supply runs out: October 1, 2026
Days from dispensing to the reminder: 25
Days covered: 30

Step by step

1Values used
2Refill timing
3Order the refill by= 2026-09-26
4Supply runs out= 2026-10-01
5Days from dispensing to the reminder= 25
6Days covered= 30

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

How early can a prescription be refilled?

Most insurers allow refills once about 75 to 80% of the previous supply has elapsed.

What about controlled medicines?

They usually have tighter early-refill rules and may not be dispensed ahead of time at all.