How many half-lives until less than 1% remains?

After 7 half-lives: (0.5)^7 = 0.78% remains. So 7 half-lives reduces the amount to less than 1% of the original.

Does this work for drug elimination?

Yes. Drugs eliminated by first-order kinetics follow the same math. A drug with a 4-hour half-life is essentially gone after 5-7 half-lives (20-28 hours).

Yes. After 2.5 half-lives, the remaining fraction is (0.5)^2.5 = 0.177 = 17.7%. The formula works for any non-negative value of n.

Free Half-Life Remaining Calculator

Calculate the remaining amount of a substance after a given number of half-lives have elapsed.

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Initial Amount

Number of Half-Lives Elapsed

Amount Remaining

3.1250

Percent Remaining3.1250 %

Amount Decayed96.8750

Amount Remaining vs Initial Amount

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Remaining After n Half-Lives

Each half-life reduces the remaining amount by half. After n half-lives, the fraction remaining is (1/2)^n.

Formula

N = N0 × (1/2)^n

This applies to radioactive decay, drug elimination, chemical degradation, and any first-order process.

Example Calculation

Starting with 100 grams, after 5 half-lives.

01Remaining = 100 × (0.5)^5
02Remaining = 100 × 0.03125 = 3.125 grams
03Only 3.125% remains after 5 half-lives

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Understanding Molarity

Learn what molarity is, how to calculate it, and why it matters in chemistry. Covers moles, liters, dilution, and step-by-step examples for preparing solutions.

Free Half-Life Remaining Calculator

Remaining After n Half-Lives

Formula

Example Calculation

Frequently Asked Questions

Understanding Molarity

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