Inhaler days left

An inhaler does not rattle when it is getting low. The counter on the side is the only honest gauge, and it counts puffs, not days. Put in the number it shows and how you use it, and this gives you the date it runs out.

Trust the counter, not the weight

An inhaler can keep spraying after its labelled number of doses, and what comes out then may not be a full dose. That is why the counter matters, and why listening to the canister when you shake it, or floating it in water, tells you nothing reliable about what is left. If yours has no counter, ask your pharmacist how to keep track of it.

Priming and extra puffs

Some inhalers need test sprays when new or after a few days unused, and those come off the same total. If you prime yours, the counter already reflects it; if you are working from the label instead, take the priming puffs off before you start.

Relievers are an average

A preventer used every day runs out on a predictable date. A reliever does not, so the date here is only as good as your average. If you find yourself needing a reliever more often than usual, that is worth telling your doctor about in its own right, not just a reason to reorder sooner.

The same arithmetic for tablets is the refill date calculator, and the inhaler write-up goes through the counting in more detail.

Common questions

How long does a 200-puff inhaler last?

Divide the puffs by how many you use a day. At 2 puffs twice a day, that is 4 a day, so 200 puffs last 50 days. At 2 puffs once a day, they last 100 days.

How do I know when my inhaler is empty?

Use the dose counter on the inhaler. It counts down from the labelled number of puffs, and the inhaler should be replaced when it reaches zero even if it still sprays, because the later sprays may not contain a full dose.

When should I reorder my inhaler?

About a week before the last full day, or earlier if your pharmacy usually needs longer. For a reliever, reorder sooner rather than later, because the days you need it most are the days it runs out fastest.

One thing this cannot do

This is an arithmetic tool, not medical advice. It works out numbers from what you type in — it does not know your medication, your prescription, or what you should do if something goes wrong. Anything about changing a dose, spacing doses differently, or handling a missed dose is a question for your doctor or pharmacist.