Half-Life Calculator - calculatorsee.com


Half-Life Calculator

Calculate remaining quantity, half-life constant, decay rate, or elapsed time for radioactive isotopes and pharmaceutical drug elimination.

Calculator Inputs

Starting amount or concentration.
hrs
Time for half to decay.
hrs
Total duration passed.

Calculated Results

Remaining Substance Quantity
12.50 mg (12.5%)
Decay Constant (lambda) 0.1216 per hr
Number of Half-Lives Elapsed 3.0 Half-Lives
Fraction Remaining 1/8 (12.5%)
Values calculate live as you adjust inputs.

About Half-Life Calculator

Models exponential radioactive decay or pharmacokinetics drug clearance where substance halves at uniform intervals.

What is Half-Life Calculator?

Models exponential radioactive decay or pharmacokinetics drug clearance where substance halves at uniform intervals.

How to Use This Calculator

  1. Enter starting quantity N0.
  2. Enter known half-life period.
  3. Enter elapsed observation time.
  4. View remaining amount and decay constant.

The Mathematical Formula & Variables

N(t) = N0 * (1/2)^(t / t_half)

Step-by-Step Worked Example

Scenario: 100 mg of drug with 5.7-hour half-life after 17.1 hours.

  1. Elapsed half-lives = 17.1 / 5.7 = 3.
  2. Remaining = 100 * (1/2)^3 = 100 * 0.125 = 12.5 mg.

Result: 12.50 mg

Frequently Asked Questions

How many half-lives until a substance is virtually gone?

In pharmacology and radiation safety, 5 half-lives clears ~97% of a substance, and 7 half-lives clears >99%.