Science Calculator Grade 9–12 With Steps

Half-Life Calculator with Steps

Use this free half-life calculator to calculate remaining amount, initial amount, elapsed time, or half-life. This tool is useful for radioactivity, nuclear chemistry, carbon dating, medicine decay, and exponential decay problems.

Calculate Half-Life

Result:
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What is Half-Life?

Half-life is the time required for half of a substance to decay or change. After one half-life, 50% remains. After two half-lives, 25% remains. After three half-lives, 12.5% remains.

N = N0 × (1/2)t/T
  • N = remaining amount
  • N0 = initial amount
  • t = elapsed time
  • T = half-life

Worked Example

A radioactive sample starts with 100 g. Its half-life is 5 years. How much remains after 10 years?

N = 100 × (1/2)10/5
N = 100 × (1/2)2 = 25 g

The remaining amount is 25 g.

Practice Question

A sample starts with 80 g. Its half-life is 4 years. How much remains after 8 years?