# Prescription Refill Calculator

URL: https://speedycalculator.com/calculators/health/prescription-refill/
Last updated: 2026-10-30

> The prescription refill calculator works out how many days your medicine will last from the quantity dispensed and how many you take a day, the date you will run out and when to request a refill.

## Inputs

- Date filled
- Quantity dispensed
- Tablets (or units) per dose
- Doses per day
- Remind me this many days before

## Results

- Days supply
- Supply runs out
- Request a refill by
- Typical earliest refill (80% used)
- Days of medicine left

## Formula

```
Days supply = quantity ÷ (units per dose × doses per day)
Run-out date = fill date + days supply
Refill reminder = run-out date − reminder days
```

## Explanation

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

FieldWhat to enterDate filledA dateQuantity dispensedA numberTablets (or units) per doseA numberDoses per dayA numberRemind me this many days beforeA 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.*

## 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.

## FAQ

**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.


## Sources

- [FDA – Medication refills and safe use](https://www.fda.gov/drugs/)