Half-Life Calculator

Any unit — grams, percent, Bq — as long as the remaining amount uses the same one.
Any time unit (years, days, hours) — elapsed time uses the same unit.
Ignored in 'Elapsed time' mode — it is the value being solved for.
Only used in 'Elapsed time' mode. Ignored in forward mode.
Worked example result
Remaining amount25.00000
Percent remaining25.000%
Half-lives elapsed2.0000
Elapsed time10.00000

Starting with 100 units and a 5-unit half-life, after 10 units of time (two half-lives) exactly 25 remain — 25%.

N = N₀ × (½)^(t ÷ t½); t = t½ × log₂(N₀ ÷ N) · Powered by CalcHub — Half-Life Calculator