Health & fitness · Medication math
Refill date calculator.
Enter the fill date and days supply to see the last day covered, the first day with none left, and the earliest refill date at the percent your plan uses.
Not medical advice
This tool only does arithmetic on numbers you type in from your own prescription or package label. It does not recommend any drug, dose or schedule. Follow your prescriber, pharmacist and the label, and ask them before changing how you take any medicine.
Inputs
Refill dates
Enter the numbers above.
How the refill date is worked out
The fill day counts as day 1. A 30-day supply filled on 1 Oct 2026 covers 1 Oct to 30 Oct, so the first day with none left is 31 Oct. Many insurance plans and pharmacies will not process a refill until a set share of the supply should have been used. That share is set by the plan, not by this tool, so you type it in. At 75 percent of 30 days, 22.5 rounds up to 23 days, which puts the earliest refill at 24 Oct 2026.
Worked example. Filled 1 Oct 2026, 30 days supply, 75 percent. Last day covered: Fri 30 Oct 2026. First day with none left: Sat 31 Oct 2026. Earliest refill: Sat 24 Oct 2026, which is 7 days before the supply ends. If today is 20 Oct, the supply has 11 days left and the refill window opens in 4 days.
Early-refill rules also vary with controlled substances and with plan exceptions such as travel or vacation overrides. Ask your pharmacy; they see the plan rules and you do not.
Frequently asked questions
How do I calculate my refill date?
Add the days supply to the fill date. The fill day is day 1, so a 30-day supply filled on 1 October is used up after 30 October and the first day with none left is 31 October.
How early can I refill a prescription?
It depends on your plan and pharmacy. This tool takes the percent of the supply they expect you to have used and counts forward. The 75 percent default is only an example, so replace it with the rule your plan gives you.
Why does the earliest date round up?
A part day is not a used day. 75 percent of 30 days is 22.5 days, so the tool counts 23 whole days from the fill date.
Can I ask for a refill sooner than the date shown?
Sometimes. Plans may allow travel or vacation overrides. Ask your pharmacist, because the tool cannot see your plan.
Sources
Checked
Pure arithmetic; the early-refill percent is whatever your plan states. Runs entirely in your browser. Nothing you type is sent or stored.
Scope
Plan rules, controlled-substance rules and exceptions differ and are not modelled here. This is a calculation aid, not medical or pharmacy advice, and it does not know your medicine, your health or your prescription. Your label, prescriber and pharmacist decide.