30-Day Refill Calculator
The 30-day supply is the default prescription length at most US pharmacies. Enter your fill date below - the calculator is already preset to 30 days and shows when your next refill comes due.
Refill Date Calculator
A 30-day supply is not a calendar month
Insurance systems and pharmacy software count days, not months. A "one month" prescription dispensed on the 6th does not renew on the 6th of the next month - it renews 30 days later, which lands on a different date depending on whether the month has 28, 30, or 31 days. Over a year this mismatch quietly moves your pickup day around the calendar, which is exactly the drift a refill calculator exists to track. If you take several medications, the drift also un-aligns them from each other, one argument for asking your pharmacy about refill synchronisation.
Your early-refill window on a 30-day fill
Most plans let you collect a refill a few days before the supply runs out. Worked example from this calculator: fill a 30-day prescription on April 6, 2026 with a 3-day early allowance and the next refill date is May 03, 2026, day 27 of the supply. Exact allowances differ - some insurers use a percentage-of-days-used rule instead of a flat number of days, and controlled substances are handled more strictly - so adjust the early-refill field to match what your pharmacy tells you.
How 30-day fills add up over a quarter and a year
For a 90-day treatment plan filled in 30-day supplies, the calculator returns 2 refills after the first fill, with the last supply running out around Jul 05, 2026. Extend that to a full 365 days and the same math produces 12 refills on top of the initial fill - a pharmacy visit roughly every month. Many people on stable maintenance medication eventually switch to 90-day supplies for that reason; the 90-day preset page runs the comparison.
Confirming the days supply from the quantity
The label's days supply is quantity divided by daily doses, and it is worth sanity-checking. Sixty tablets taken twice a day is 30 days; ninety capsules taken three times a day is also 30 days. When a dose changes mid-supply - say your prescriber doubles the daily amount - the true days supply halves, and your refill date moves up. Recalculate with the new dose rather than trusting the old label.
Informational tool only: refill policies, early-fill rules, and insurance limits vary widely. Confirm your actual refill date with your pharmacist or prescriber before planning around it.
30-Day Refill Questions
Is a 30-day supply the same as one month?
No. Pharmacy and insurance systems count 30 days from the fill date, while calendar months run 28 to 31 days. A prescription filled on the 6th of one month is usually due 30 days later, not on the 6th of the next month. The gap is small each cycle but accumulates over a year, which is why refill dates wander around the calendar.
How early can I refill a 30-day prescription?
It depends on your plan, but with the common 3-day early allowance this calculator puts the window at day 27: a fill on April 6, 2026 becomes refillable on May 03, 2026. Some insurers use percentage-based rules instead of flat days, and controlled substances get shorter windows, so check with your pharmacy before making the trip.
How many 30-day refills cover a 90-day treatment plan?
Per this calculator, a 90-day plan in 30-day supplies needs 2 refills after the first fill, with the final supply lasting until about Jul 05, 2026 in the worked example. If your prescriber intends longer-term treatment, ask whether the prescription was written with enough refills to avoid a renewal gap.
How many 30-day fills do I need in a year?
Covering 365 days in 30-day supplies takes 12 refills after the initial fill according to this calculator's math. That is a monthly pharmacy trip; if your medication is a stable maintenance therapy, a 90-day supply cuts the visits to a quarter as many.
Can I switch from a 30-day to a 90-day supply?
Often, but it requires a new prescription written for the longer quantity and a plan that covers it. Mail-order pharmacies and many retail chains support 90-day fills for maintenance medications. Raise it with your prescriber at your next appointment - the switch cannot be made by the pharmacy on its own.
Other prescription lengths
Related reading
Need a different supply length?
The main refill calculator accepts any days-supply value and also includes a days supply calculator for working out how long a quantity will last.
Open the Refill Calculator