Half-Life Decay Calculator

Compute remaining quantity after any number of half-lives — isotopes, medicine, caffeine.

Starting amount:

Half-life (any unit):

Elapsed time (same unit):

How to use

Enter the starting amount, half-life and elapsed time, then click Calculate. Everything runs in your browser — nothing is uploaded or stored.

How much caffeine is left after 10 hours?

Enter 100 mg, 5 h half-life, 10 h elapsed — about 25 mg.

What counts as a half-life?

Any time unit — hours, days or years — as long as both use it.

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