Medication Days Supply Calculator

The days supply of a prescription is how long the dispensed quantity lasts at the prescribed dose. Pharmacies and insurers use it to decide when a refill can be processed, and patients use it to avoid running out — especially before travel, holidays or a change of pharmacy.

Enter the quantity dispensed (tablets, capsules, mL, puffs or units), the amount taken per dose and how many times a day you take it, then the date the prescription was filled. The calculator returns the whole number of days the supply covers, the date of your last full day of medication, the date the next fill is due and the earliest date a plan that allows refills at a set percentage used would typically approve a refill. Add remaining refills to see how long the full prescription covers.

Refill rules differ between insurers, pharmacies and countries, and controlled substances often have stricter limits. The refill threshold is adjustable — 75–80% is common in the US — so check with your pharmacist or plan for the exact rule.

Daily use is the amount per dose multiplied by the number of doses per day. Dividing the quantity dispensed by daily use gives how many full days the supply covers, rounded down because a partial day does not count as a full day of therapy. Any remainder is shown as leftover units.

Counting the fill date as day 1, the last full day of medication is the fill date plus (days − 1), and the next fill is due the day after. Many insurance plans allow a refill once a set share of the supply should have been used (often 75–80%); the earliest refill date is the fill date plus that share of the days supply, rounded up.