Calculate half-life, remaining quantity, decay constant, elapsed time, and more.
Enter any two values to calculate the third. Supports various units and real-world scenarios.
See how to use the half-life calculator in real-world scenarios.
Calculate the remaining amount of Radium-226 after 7,600 years, starting with 100 grams. Half-life is 1,600 years.
Initial Amount (N₀): 100
Remaining Amount (N): undefined
Half-Life (t₁/₂): 1600
Elapsed Time (t): 7600
Decay Constant (λ): undefined
Unit: g
Time Unit: y
Find the age of a sample if 25% of Carbon-14 remains. Half-life is 5,730 years, initial amount is 1 mol.
Initial Amount (N₀): 1
Remaining Amount (N): 0.25
Half-Life (t₁/₂): 5730
Elapsed Time (t): undefined
Decay Constant (λ): undefined
Unit: mol
Time Unit: y
How much Iodine-131 remains after 24 days if you start with 50 mg? Half-life is 8 days.
Initial Amount (N₀): 50
Remaining Amount (N): undefined
Half-Life (t₁/₂): 8
Elapsed Time (t): 24
Decay Constant (λ): undefined
Unit: g
Time Unit: d
A drug has a half-life of 6 hours. How much remains after 18 hours if the initial dose is 200 mg?
Initial Amount (N₀): 200
Remaining Amount (N): undefined
Half-Life (t₁/₂): 6
Elapsed Time (t): 18
Decay Constant (λ): undefined
Unit: g
Time Unit: h