Prescription Refill Calculator
Use this prescription refill calculator to find when your medicine runs out, the earliest date your plan may allow a refill, and when to set a reminder.
Updated October 22, 2026
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Your Prescription Refill Date Is Calculated
Your refill date depends on your days supply: the number of days your medicine lasts at the dose on your label. Most plans pay for a refill a little before you run out, once a set share of that supply has been used. This calculator works out the days supply, then counts forward from the fill date.
What a Refill Date Measures
The run-out date is the first day you would have no medicine left, if you start on the fill date and take every dose as labeled. The earliest refill date is the first day your plan may pay for the next fill. Medicare drug plans call this limit a "refill-too-soon" edit, and each plan sets its own and can relax it in an emergency¹. The result is a date, not dosing advice.
The Formula
Days supply = quantity dispensed ÷ (amount per dose x doses per day), rounded down to whole days
Run-out date = date filled + days supply
Earliest refill date = date filled + (days supply x threshold %), rounded up to a whole day
Reminder date = run-out date minus your reminder days, but not before the earliest refill date
Pharmacies bill the days supply that the directions and quantity on the prescription support².
How This Calculator Computes Your Result
Enter the date filled. If your label or pharmacy receipt shows a days supply, enter it directly, since that is the number your plan uses. Otherwise enter the quantity, the amount per dose and how often you take it:
How often | Doses a day |
Once, twice, three or four times a day | 1, 2, 3 or 4 |
Every 4, 6, 8 or 12 hours | 6, 4, 3 or 2 |
Every other day | 0.5 |
Once a week | 1/7 |
As needed | The most doses a day your label allows |
Every 8 hours means 3 doses in 24 hours, for example 6 am, 2 pm and 10 pm, so it uses up your supply at the same rate as three times a day. For as-needed medicine, the tool counts the most you may take in a day. Some plans will not pay for a prescription that says only "as needed" and ask for the maximum daily use instead².
Then pick a threshold (75% by default) and a reminder lead (7 days by default). Each date shows with its weekday, and you can add the dates to your calendar. For example, 100 capsules taken every 8 hours from October 5, 2026 last 33 days, run out on November 7, and reach 80% on November 1.
What Your Result Means
The threshold is the share of the days supply that must pass before a refill. Here is where each setting lands, counting days after the fill date:
Threshold | 30-day fill | 90-day fill | Example plan rules |
75% | Day 23, with 7 days left | Day 68, with 22 days left | Medi-Cal Rx (except opioids), Mississippi Medicaid (non-controlled drugs), a North Carolina retiree Medicare plan³ ⁴ ⁵ |
80% | Day 24, with 6 days left | Day 72, with 18 days left | Wisconsin Medicaid listed drugs, 10 to 34 day fills (2022 table)⁶ |
85% | Day 26, with 4 days left | Day 77, with 13 days left | Mississippi Medicaid, Schedule III to V drugs⁴ |
90% | Day 27, with 3 days left | Day 81, with 9 days left | Medi-Cal Rx, opioids³ |
The day count rounds up, so 75% of 30 days (22.5) becomes day 23. Plans differ, and your pharmacy can tell you your plan's number. Some plans also add up early refills over time: Medi-Cal Rx rejects a refill once early refills pass 20 days within 180 days³.
Controlled Substance Refill Rules
Federal law sets extra limits for controlled substances, the drugs the DEA places in Schedules II to V:
Schedule | Federal refill rule |
II | "The refilling of a prescription for a controlled substance listed in Schedule II is prohibited." A prescriber may write several prescriptions for up to a 90-day supply in total, each marked with the earliest date it may be filled⁷. |
III and IV | No fill or refill "more than six months after the date on which such prescription was issued", and no more than five refills. After that, a new prescription is needed⁸. |
V | No federal limit on the number or timing of refills. The drug may be dispensed only "for a medical purpose"⁹. |
State laws and plans can be stricter. The DEA notes: "Some states and many insurance carriers limit the quantity of controlled substances dispensed to a 30-day supply"¹⁰. For Schedule III and IV, the tool shows the six-month limit date and which refills fall before it. A 90-day Schedule IV prescription written and filled September 1, 2026 has a limit of March 1, 2027, so only 2 of 5 refills fit (November 30 and February 28).
Vacation Supplies and 90-Day Fills
The optional trip check compares your travel dates with your supply. If your earliest refill date falls before you leave, a normal refill may cover the trip. If not, it shows how many days you would be short. A 30-day fill on October 1, 2026 lasts through October 30, with an earliest refill (75%) of October 24, so a trip from October 20 to November 10 leaves about 11 days uncovered.
Vacation supplies are a plan decision. Medi-Cal Rx allows a vacation override once within 365 days³, and one North Carolina retiree plan offers an extended supply for 90 days or more abroad if asked 30 days ahead⁵. That plan also suggests ordering a 90-day refill when no more than 14 days remain⁵. A longer reminder helps with mail order, where shipping takes time.
A Note on Accuracy
The date math is exact, but the result is only as good as the numbers you enter. Your plan uses the days supply the pharmacy billed, its own threshold, and sometimes your refill history, so these dates are estimates to confirm with your pharmacy. Eye drops, inhalers, insulin and creams rarely divide evenly into doses, so the days supply on the label works best for them. This calculator does not replace your prescription label, your prescriber or your pharmacist.
Frequently Asked Questions
How early can you refill a prescription?
Many plans allow a refill once 75% of the days supply has passed, which is day 23 of a 30-day fill³ ⁴ ⁵. Some use 80% to 90%, often for controlled substances.
When can I refill a 90-day prescription?
At a 75% threshold, the earliest refill is 68 days after the fill date, with 22 days of medicine left. A plan with a higher threshold will make that date later.
Can Schedule II prescriptions be refilled?
No. Federal law prohibits refills of Schedule II prescriptions, though a prescriber may issue several prescriptions covering up to 90 days, each with the earliest date it may be filled⁷.
Is this prescription refill calculator accurate?
The dates are calculated exactly from what you enter, but each plan sets its own refill rule. Treat the results as estimates and confirm with your pharmacy.
Sources
Information Related to Coronavirus Disease 2019 (COVID-19), CMS, 2020
Specific Directions Requirement for All Prescriptions, Indiana Health Coverage Programs, 2026
Updates to the Early Refill Policy, Medi-Cal Rx, 2026
Refills/Renewals of Prescription Drugs (23 Miss. Code R. 214-1.7), Mississippi Division of Medicaid, 2016
Refill Guidelines for Medicare Retirees 70/30 Plan, North Carolina State Health Plan
Early Refill Drugs, Wisconsin ForwardHealth, 2022
21 CFR 1306.12, Refilling Prescriptions, Drug Enforcement Administration
21 CFR 1306.22, Refilling of Prescriptions, Drug Enforcement Administration
21 U.S.C. 829, Prescriptions, US Code
Pharmacist's Manual, DEA Diversion Control Division, 2022