Running out of a regular medicine can be dangerous, especially for heart, seizure or mental health medicines. Many insurers allow refills when about 75–80% of the supply has been used.
How to use the Prescription Refill Calculator
- Date filled
- Quantity dispensed
- Tablets (or units) per dose
- Doses per day
- Remind me this many days before
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the fill date, quantity and how you take the medicine.
Inputs explained
| Field | What to enter |
|---|---|
| Date filled | A date |
| Quantity dispensed | A number |
| Tablets (or units) per dose | A number |
| Doses per day | A number |
| Remind me this many days before | A number |
What each result means
- Days supply = [Quantity dispensed]÷([Tablets (or units) per dose]×[Doses per day])
- Supply runs out = [Date filled] + floor([Days supply])
- Request a refill by = [Supply runs out] – [Remind me this many days before]
- Typical earliest refill (80% used) = [Date filled] + floor([Days supply]×0.8)
- Days of medicine left = max([Supply runs out] – today(), 0)
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Days supply = quantity ÷ (units per dose × doses per day)
Run-out date = fill date + days supply
Refill reminder = run-out date − reminder days
Worked example
Inputs — Date filled: 2026-10-05; Quantity dispensed: 90; Tablets (or units) per dose: 1; Doses per day: 1; Remind me this many days before: 7.
Results — Days supply = 90 days; Supply runs out = Sun, January 3, 2027; Request a refill by = Sun, December 27, 2026; Typical earliest refill (80% used) = Wed, December 16, 2026; Days of medicine left = 64 days.
Key terms
- Days supply
- Number of days a prescription lasts.
Frequently asked questions
When can I refill my prescription?
Often once about 75–80% of the supply has been used; check with your pharmacy or insurer.
What if I take extra doses?
Your supply will run out sooner – recalculate with your real usage.
Can I get an emergency supply?
Pharmacists in many places can supply a short emergency amount.