Days Supply Calculator: How Long Will My Pills Last?

How to use the calculator

1. Enter how many tablets, capsules or doses you have. For a new bottle, that's the quantity on the label. Mid-bottle, count what's left.
2. Enter how many you take each time. Use 0.5 if you take half a tablet, or 2 if you take two at once.
3. Pick how often you take it.
4. Add the first day you'll take them, or leave it blank to count from today. If you've already taken today's doses, set it to tomorrow.

How the math works

The calculator works out how many doses you have (pills divided by the amount per dose), then how many days those doses cover at your schedule. Partial days are dropped, because a day where you can't take every dose isn't a covered day. Your start date counts as day one.

Two examples you can check by hand: 30 tablets taken one at a time twice a day last 15 days. Four tablets taken once a week last 28 days.

When to ask for a refill

The calculator suggests asking for a refill a week before you run out. That's a planning buffer for weekends, holidays and a doctor who needs to approve a new prescription. It isn't a pharmacy or insurance rule. Your plan decides how early it will pay for a refill, and some medicines have tighter rules. Under federal law, Schedule II controlled substances can't be refilled at all, and Schedule III and IV prescriptions can be refilled no more than five times within six months of being written.

If you're out of refills, your doctor needs to approve more, so that buffer matters even more. As the National Institute on Aging puts it, your doctor can tell you if you need a refill, so ask at your next visit rather than when the bottle is empty.

When the numbers don't add up

If you're running out sooner than the calculator says, something changed. A dose may have been doubled, a pill may have been dropped, or pills may have ended up in the wrong bottle or organizer slot. A refill can also look different from your last one when the pharmacy switches manufacturers. Don't guess with a pill you aren't sure about. Our guide to why a refill can look different explains what to check, and your pharmacist can confirm what you have. If you juggle several medicines, MedlinePlus notes that a pill organizer may help you keep doses straight.