Half-Life Calculator

Last Updated on March 2, 2026 | 2 : 22 pm by Anas Brittany

Use this half-life calculator to determine how much of a substance remains after a certain time, how long decay takes, or the half-life of a material. Enter any known values and the calculator will apply the exponential decay formula instantly.

What Is Half-Life?

Half-life is the time it takes for a substance to decrease to half of its original amount. It is commonly used to describe radioactive decay, but it also applies to chemical reactions, biological processes, and drug metabolism.

For example, if a substance has a half-life of 10 years, only half of it will remain after 10 years. After another 10 years, half of the remaining amount will be left.

Half-Life Formula

The basic half-life equation is:

N = N₀ × (1/2)^(t / T)

Where:

• N = remaining amount
• N₀ = initial amount
• t = elapsed time
• T = half-life

This formula shows exponential decay over time.

Example Calculation

Initial amount = 100 grams
Half-life = 5 years
Time = 10 years

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

Where Half-Life Is Used

Half-life calculations are important in:

• Radioactive decay and nuclear science
• Medicine and drug dosing
• Carbon dating and archaeology
• Environmental science
• Chemistry and biology

Understanding Exponential Decay

Half-life is different from linear change. The amount decreases by a percentage, not by a fixed amount. Each period reduces the remaining quantity by half.

Frequently Asked Questions

Does half-life ever reach zero?

No. In theory, the amount decreases forever but never reaches exactly zero.

Can half-life be used for medications?

Yes. Half-life is commonly used to determine how long a drug stays active in the body.

Is half-life always constant?

For radioactive materials, the half-life is constant and does not change based on conditions.