Medication Days Supply and Refill Date Calculator

How long a prescription lasts and the date to order a refill. Free, private and instant.

How to use the Days Supply Calculator

  1. Enter quantity dispensed (units).
  2. Enter amount per dose (units).
  3. Enter doses per day.
  4. Pick date you started this supply.
  5. Choose remind me to refill: 3 days before, 5 days before, 7 days before or 10 days before.
  6. Press Calculate to get an instant result with a colour scale, chart and plain-English explanation.

About the Days Supply Calculator

Days supply is the number of days a prescription will last when taken as directed. Pharmacies and insurers use it to decide when a refill can be dispensed, and knowing your run-out date helps you avoid missed doses. Enter the quantity dispensed, the amount per dose and how many doses you take per day to get the days supply, the run-out date, a refill reminder date and how much should be left today.

Also known as: days supply calculator, prescription refill date calculator, pill count calculator.

Worked example

Dates in this example are worked out as if today were 5 Nov 2026.

Days supply: 15 days (1 to 4 weeks). 30 units at 2.00 per day last 15 days. Your supply runs out on 20 Nov 2026; order a refill by 13 Nov 2026.

Formula and cut-offs

Days supply = quantity dispensed / (amount per dose x doses per day), rounded down to whole days. Run-out date = start date + days supply. Refill date = run-out date - reminder days. Example: 60 tablets, 1 tablet twice a day = 60 / 2 = 30 days.

Frequently asked questions

How do you calculate days supply?

Divide the total quantity dispensed by the amount taken per day. For example, 90 tablets taken one at a time, three times a day, is 90 / 3 = 30 days.

When can I refill my prescription?

Many pharmacies and insurers allow a refill once about 75 to 80% of the days supply has passed, for example from day 23 of a 30-day supply. Rules differ by country, plan and medicine.

Is a 90-day supply cheaper?

Often yes. For long-term medicines a 90-day supply usually costs less per dose and means fewer pharmacy trips. Compare prices before you buy.

How do I calculate days supply for liquids or inhalers?

Use the total volume or number of puffs as the quantity and the mL or puffs per dose as the amount per dose. Check the device's dose counter as well.

Sources and references

Written and checked by the MediHub editorial team against the sources above. Read how we build and review our calculators.

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Last updated . This calculator is for education only and is not medical advice. See the medical disclaimer.