Prescription Refill Calculator: When Can I Refill?
Last reviewed: July 2026
Use this prescription refill calculator to estimate your next refill date from your last fill date, days supplied, and refill timing rule. It works for common 28-day, 30-day, 60-day, and 90-day supplies. Your pharmacy, prescriber, insurance plan, medication type, and local rules may affect the final refill date.
Choose the right refill planning tool
Start with the refill date calculator, or use a more specific page when your question is about days supply, pills left, insurance timing, or a refill-too-soon message.
How do you calculate a prescription refill date?
To estimate a refill date, start with the fill date and days supplied, then apply the refill timing rule. For example, if a 30-day supply can be refilled after 75% is used, the estimated refill point is around Day 23. If the rule is 80%, the estimated refill point is around Day 25.
Learn how refill timing math worksCommon refill date examples
| Supply | Refill timing | Approximate refill point | Example use |
|---|---|---|---|
| 28-day supply | 75% used | around Day 21 | common short-cycle estimate |
| 30-day supply | 75% used | around Day 23 | common early-refill estimate |
| 30-day supply | 80% used | around Day 25 | stricter common estimate |
| 60-day supply | 75% used | around Day 45 | longer supply estimate |
| 90-day supply | 75% used | around Day 68 | mail-order or maintenance estimate |
| 90-day supply | 80% used | around Day 72 | stricter maintenance estimate |
These are planning examples only. Actual refill timing can vary by pharmacy, insurance plan, medication, prescriber instructions, and state rules.
Refill date formula
Estimated refill day = fill date + ceiling(days supplied x refill percentage).
- 30 days x 75% = 22.5, rounded to about Day 23.
- 30 days x 80% = 24, around Day 25 depending on counting method.
- 90 days x 75% = 67.5, rounded to about Day 68.
More prescription refill calculators
Why your actual refill date may be different
This calculator gives a planning estimate only. The final refill date is the date your pharmacy, prescriber, insurance plan, and applicable rules allow the refill to be processed.
Prescription refill calculator FAQ
When can I refill my prescription?+
You can use this calculator to estimate a refill date from the last fill date, days supplied, and a refill timing percentage. Your pharmacy, prescriber, insurance plan, medication type, and local rules can change the final date.
How early can you refill a 30-day prescription?+
As a planning example, a 30-day supply at 75% used estimates around Day 23. At 80% used, it estimates around Day 25 depending on the counting method.
What does the 75% refill rule mean?+
A 75% timing rule means the estimate starts when about three quarters of the current supply has been used. For a 30-day supply, 30 x 75% equals 22.5 days, rounded to about Day 23.
What does the 80% refill rule mean?+
An 80% timing rule means the estimate starts when about four fifths of the current supply has been used. For a 30-day supply, that is about 24 days, or around Day 25 when the fill date counts as Day 1.
Can I refill a 90-day prescription early?+
This calculator can estimate common 90-day timing examples, such as 75% used around Day 68 or 80% used around Day 72. Confirm the actual date with your pharmacy or insurance plan.
Is this the same as my pharmacy's refill date?+
No. This is a date-math estimate. Pharmacy systems may account for plan rules, medication type, prescriber instructions, stock, local rules, or pharmacist judgment.
Why does my pharmacy say refill too soon?+
A refill-too-soon message often means the pharmacy or insurance system is using a different timing rule, counting method, or plan edit than your estimate. Ask the pharmacy or insurance plan to confirm the date they see.
Can controlled substances be refilled early?+
Controlled-substance timing can be affected by federal law, state law, prescriber instructions, pharmacy policy, PDMP review, and pharmacist judgment. Use any estimate as a planning reference only.
Does insurance always use the same refill rule?+
No. Timing rules can vary by plan, pharmacy network, medication, supply length, refill history, and other edits. The percentage you choose here is only a planning input.
Should I call my pharmacy to confirm?+
Yes. If timing matters, call your pharmacy or insurance plan to confirm the final refill date before making travel, payment, or medication plans.
Free printable resources
Print free planning tools for refill dates, medication tracking, pill counts, and days-supply math. These resources are designed for caregivers, patients, and pharmacy learners.
About this calculator
RefillDateCalculator.org provides date-math tools for prescription refill planning. The calculator estimates dates from fill date, days supplied, and refill timing rules. It is not medical, legal, insurance, or dispensing advice.
This calculator estimates dates using basic days-supply math. It does not decide whether a prescription can be legally, clinically, or operationally refilled. Final refill availability depends on your prescriber, pharmacy, insurance plan, medication type, state rules, and pharmacist judgment.