30-Day Prescription Refill Calculator
Use this 30-day prescription refill calculator to estimate your next refill date from your last fill date and refill timing rule. For many 30-day supplies, a 75% timing rule lands around Day 23, while an 80% rule lands around Day 25 depending on the counting method. Your pharmacy, prescriber, insurance plan, medication type, and local rules may affect the final refill date.
When can you refill a 30-day prescription?
A 30-day supply may often be estimated by how much of the supply has been used. This calculator applies the refill timing percentage you choose and turns it into a calendar date.
A 75% timing rule is around Day 23. An 80% timing rule is around Day 25 depending on how days are counted.
The actual refill date can differ by pharmacy, insurer, prescriber, medication, and local rules. Treat the result as a planning estimate.
Why do some 30-day refills show Day 23 or Day 25?
Different systems may count dates slightly differently. The calculator shows the estimated calendar date based on the selected counting method.
- 75% of 30 days = 22.5 days, commonly rounded to about Day 23.
- 80% of 30 days = 24 days, commonly around Day 24-25 depending on whether the fill date is counted as Day 1.
Because pharmacies and insurance systems may use different date-counting rules, treat the result as a planning estimate.
30-day refill date formula
Estimated refill point = 30 days x refill timing percentage.
- 30 x 75% = 22.5 days, about Day 23.
- 30 x 80% = 24 days, about Day 24-25 depending on counting method.
- 30 x 85% = 25.5 days, about Day 26.
- 30 x 90% = 27 days, about Day 27.
30-day refill timing examples
| Refill timing | Math | Approximate refill point | What it means |
|---|---|---|---|
| 75% used | 30 x 0.75 = 22.5 | around Day 23 | common early-refill estimate |
| 80% used | 30 x 0.80 = 24 | around Day 24-25 | stricter common estimate |
| 85% used | 30 x 0.85 = 25.5 | around Day 26 | later refill estimate |
| 90% used | 30 x 0.90 = 27 | around Day 27 | very conservative estimate |
| Full supply | 30 x 1.00 = 30 | around Day 30/31 | no early refill estimate |
These examples are for planning only. Actual refill timing can vary by pharmacy, insurance plan, medication, prescriber instructions, and state rules.
Example: 30-day prescription filled on June 1
If a 30-day prescription was filled on June 1, a 75% estimate falls around Day 23, and an 80% estimate falls around Day 24-25 depending on whether the fill date is counted as Day 1. With the calculator's default Day 1 counting, 75% estimates June 23 and 80% estimates June 24. The calculator uses your selected counting method to estimate the calendar date.
Related refill calculators
Why your 30-day refill date may be different
30-day prescription refill FAQ
How early can I refill a 30-day prescription?+
A 30-day prescription can be estimated with the percent-used timing rule you choose. A 75% estimate is around Day 23, while an 80% estimate is around Day 24 to Day 25 depending on counting method.
What is the 75% rule for a 30-day prescription?+
The 75% rule means about three quarters of the 30-day supply has been used. Since 30 x 0.75 equals 22.5, the estimate commonly lands around Day 23.
What is the 80% rule for a 30-day prescription?+
The 80% rule means about four fifths of the supply has been used. Since 30 x 0.80 equals 24, the estimate is commonly around Day 24 to Day 25 depending on whether the fill date counts as Day 1.
Is Day 23 or Day 25 the right refill day?+
Neither day is universal. Day 23 is a common 75% estimate, and Day 25 is a common 80% estimate when the fill date counts as Day 1. Your actual date may differ.
Can I refill a 30-day prescription after 28 days?+
A Day 28 estimate is closer to a conservative 90% timing rule for a 30-day supply. Whether a refill can be processed depends on the pharmacy, prescriber, insurance plan, medication, and local rules.
Why does my pharmacy say refill too soon?+
A refill-too-soon message may mean 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 their date.
Does every insurance plan use the same refill rule?+
No. Timing rules can vary by plan, pharmacy network, medication type, supply history, and other edits. Use this calculator as a planning estimate only.
Can controlled substances follow the same 30-day refill estimate?+
The estimate may not apply. Final timing for controlled substances can depend on federal law, state law, prescriber instructions, pharmacy policy, PDMP review, and pharmacist judgment.
What if I lost my medication or need a vacation refill?+
Lost medication and vacation situations can involve pharmacy or insurance override processes. Contact your pharmacy or insurance plan for the options that apply to your prescription.
Should I call my pharmacy to confirm the date?+
Yes. If the refill timing matters, confirm the final date with your pharmacy or insurance plan before making travel, payment, or medication plans.
About this 30-day refill calculator
This calculator uses basic days-supply math to estimate refill timing for a 30-day supply. It is designed for planning and education only. 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.