Half-Life Calculator

Half-life is the time required for a quantity to reduce to half its initial value. This calculator supports drug elimination tracking, radioactive decay calculations, and general exponential decay scenarios.

Quick presets:
Leave blank to calculate for the current time

Important Disclaimer

The half-life data provided by this calculator is for general informational and educational purposes only. It should not be used as a substitute for professional medical advice, diagnosis, or treatment. Individual metabolism, drug interactions, organ function, age, and other factors can significantly affect how substances are eliminated from the body. Always consult a qualified healthcare provider before making any decisions about medications. See full terms and conditions.

About Half-Life

Half-life is the time required for a quantity to reduce to half its initial value. This calculator supports drug elimination tracking, radioactive decay calculations, and general exponential decay scenarios.

The Formula: N(t) = N₀ × (1/2)^(t/t½), where N₀ is the initial amount, t is elapsed time, and t½ is the half-life.

Multiple Doses: When multiple doses are taken at different times, the calculator tracks each dose independently and sums their remaining concentrations to show the total amount in the system.

Popular Calculations
Caffeine after 10 hours Tylenol after 8 hours Carbon-14 after one half-life Ibuprofen after 6 hours Iodine-131 after 16 days Nicotine after 4 hours Aspirin after 1 hour Radon-222 after 1 week

Mathematical Explanation

The half-life formula N(t) = N₀ × (1/2)^(t/t½) describes exponential decay, where N₀ is the initial quantity, t is elapsed time, and t½ is the half-life. The decay constant λ = ln(2)/t½ provides an equivalent representation: N(t) = N₀ × e^(-λt). For multiple doses taken at different times, the total remaining concentration is the sum of each individual dose's remaining amount, calculated independently using the same decay formula from each dose's administration time.

Frequently Asked Questions

Half-life is the time it takes for half of a substance to decay or be eliminated. After one half-life, 50% remains. After two half-lives, 25% remains, and so on.

Select your medication from the dropdown or enter its half-life manually. Add each dose with the time taken, and the calculator will show the remaining concentration at any time.

Exponential decay describes processes where a quantity decreases at a rate proportional to its current value. The half-life formula is a special case of exponential decay.

Yes! Add multiple doses with different times using the 'Add Dose' button. The calculator will show individual dose curves and the combined total concentration.

The decay constant (λ) relates to half-life by λ = ln(2)/t½. It represents the probability of decay per unit time.

Resources & References

Encyclopedia Resources
  • Half-life - Comprehensive overview of half-life in physics, chemistry, and pharmacology
  • Exponential decay - Mathematical description of exponential decay processes and their applications
Educational Resources