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The Peptide Effect

Tools

Half-Life Calculator

Enter a starting amount, half-life, and elapsed time to calculate how much remains. Includes a decay timeline and the exact exponential formula.

mg
hours
hours

Remaining after 12 hours

0.2500

mg (25.0% remaining)

% remaining

25.0

%

% decayed

75.0

%

Half-lives elapsed

2.00

× 6 h

Show the math›

Formula: A(t) = A₀ × (½)^(t / t½)

A(12) = 1 × (0.5)^(12 / 6)

= 1 × (0.5)^2.0000

= 1 × 0.250000

= 0.250000 mg

Percentage: (0.250000 / 1) × 100 = 25.00%

Assumptions

  • Assumes simple first-order (exponential) decay
  • Real pharmacokinetics involve absorption, distribution, and metabolism phases that this model does not capture
  • Half-life values vary between individuals based on metabolism, body composition, and administration route
  • This is a mathematical model, not a pharmacokinetic simulation

How This Calculator Works

Flow diagram showing how the half-life calculator works
Half-life calculation flow — from peak concentration to decay timeline

The calculator uses the exponential decay formula: A(t) = A₀ × (½)^(t / t½), where A₀ is the starting amount, t is elapsed time, and t½ is the half-life. The decay timeline shows remaining amounts at each half-life interval.

Assumptions & Limitations

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Frequently Asked Questions

What is a half-life?
A half-life is the time it takes for half of a substance to be eliminated or decay. After one half-life, 50% remains. After two half-lives, 25% remains. After three, 12.5%, and so on. The decay follows an exponential curve.
How is this different from real pharmacokinetics?
This calculator models simple first-order (exponential) decay. Real drug metabolism involves absorption (how quickly the substance enters the bloodstream), distribution (how it spreads through tissues), and elimination (how the body clears it). These phases create a more complex curve than a single exponential. This tool gives a useful approximation, not a full PK model.
Where do I find the half-life for a specific peptide?
Half-life values are typically reported in research literature and vary by administration route (subcutaneous, intramuscular, intravenous). Our individual peptide profile pages list known half-life ranges where published data is available.
Can I use any time unit?
Yes — the math works with any consistent time unit. Just make sure the half-life and elapsed time use the same unit (both hours, both days, etc.). The calculator supports hours and days.

Educational Use Only

This calculator models simple exponential decay for educational purposes. It is not a pharmacokinetic simulation and should not be used for clinical dosing decisions. Consult a healthcare provider for guidance on drug metabolism and timing.

Last reviewed: February 2026