Half-Life Calculator
Calculate radioactive decay and half-life. Find remaining amount, decay constant, and time elapsed.

Use same units as half-life

Results
50.00
Remaining Amount
100.0
Initial Amount
5.730e+3
Time Elapsed
5.730e+3
Half-Life

Decay Constant

1.210e-4

Half-Lives Elapsed

1.00

% Remaining

50.00%

% Decayed

50.00%

Decay Curve
Half-Life Progression
Half-LivesTimeAmount% Remaining
15.730e+350.0050.00%
21.146e+425.0025.00%
31.719e+412.5012.50%
42.292e+46.2506.25%
52.865e+43.1253.13%

Key Formulas

N(t) = N0 * (1/2)^(t/t1/2)
N(t) = N0 * e^(-lambda*t)
lambda = ln(2) / t1/2
t = t1/2 * log2(N0/N(t))

Where:

  • N(t) = amount remaining after time t
  • N0 = initial amount
  • t1/2 = half-life
  • lambda = decay constant

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