The short answer: divide the pills you have by the number you take per day and round down to get your days of supply. Reorder when you have about seven to ten days left, not on your last pill, so a weekend or a pharmacy delay never leaves you without medicine.

Running out of a medicine is one of the most avoidable problems in taking one, and it almost always happens for the same reason: nobody was counting until the bottle was nearly empty. A little arithmetic, done once and kept current, turns "I think I have some left" into "I have eleven days, I will reorder Thursday."

Step 1: Count what you have now

Open the bottle and count the pills. That number is your starting inventory. Do it once, honestly, and you only ever have to adjust from there.

Step 2: Work out your daily rate

Multiply pills per dose by doses per day. One pill twice a day is 2 per day. Two pills three times a day is 6 per day. This is your consumption rate, and it is the number everything else depends on.

Step 3: Divide to get days of supply

Days of supply = pills you have ÷ pills per day, rounded down. Example: 40 pills at 2 per day is 20 days. 45 pills at 2 per day is 22 days, not 22.5, because you round down.

Rounding down is not fussiness. Rounding up tells you that you have a day of medicine you do not actually have, and that is precisely the mistake that leaves someone a pill short on a Sunday. When in doubt, undercount.

Step 4: Set a refill trigger with a buffer

Do not reorder on your last pill. Pick a trigger of roughly seven to ten days remaining and reorder then. That buffer absorbs the things that go wrong between "I need a refill" and "I have the medicine in my hand":

  • Weekends and holidays when the pharmacy or your doctor is closed.
  • Pharmacy processing and stock delays.
  • Insurance authorizations or a prescription that needs the doctor to renew it.
  • Travel, where you want a cushion rather than a cliff.

Step 5: Keep the count honest

An inventory is only useful if it stays current. Adjust it when you take a dose and when you pick up a refill. If the number drifts from reality, it stops being trustworthy, and an untrustworthy count is barely better than no count at all.

Where SeymourPills fits. This is the arithmetic SeymourPills does for you. Every time you tap Taken, your count goes down; it estimates your days left with the round-down rule above, and it tells you when you cross your refill trigger, before you run out rather than after. Recording a refill is one tap. It all runs on your phone. See what it does.

Common questions

How do I calculate how many days of medicine I have left?

Divide the number of pills you have by the number you take per day, and round down. For example, 40 pills at 2 pills per day is 20 days of supply. Round down so the estimate never tells you that you have a day you do not.

When should I refill a prescription?

Refill when you have roughly seven to ten days of medicine left, not on your last pill. That buffer covers weekends, holidays, pharmacy processing, and insurance or authorization delays, any of which can otherwise leave you without medicine.

Why does rounding down matter?

Rounding up can tell you that you have an extra day of medicine that you do not actually have, which is exactly the error that causes someone to run out. Always round the days-left estimate down.

This guide is general information, not medical advice, and is not specific to your prescription. Talk to your pharmacist about refill timing, quantities, and any medicine that must not be stopped or interrupted.