Peptide Half-Life Calculator
Half-life tells you how fast a compound leaves the body. From it you can work out how much remains at any time after a dose, and — if you dose repeatedly — how high levels climb and when they level off.
The formula
Remaining = dose × (½) time ÷ half-life
One half-life leaves 50%, two leaves 25%, three leaves 12.5%. After about five half-lives roughly 97% has cleared.
Worked example
Example
Dose250 mcg
Half-life6 hours
Time since dose12 hours (2 half-lives)
Remaining62.5 mcg (25%)
Single dose vs. repeated dosing
Single dose mode plots the decay curve and the amount left at the time you enter. Repeated dosing mode stacks each new dose on what hasn't cleared, then reports the accumulation factor, the steady-state peak and trough, and the time to reach steady state — with a chart of the rising sawtooth.
How to use the calculator
- Enter the dose and the half-life (hours or days).
- For a single dose, enter the time elapsed to see what's left.
- Switch to repeated dosing and enter an interval to see accumulation and steady state.
Frequently asked questions
How is half-life used to find how much is left?
Each half-life halves the remaining amount. After n half-lives, one half raised to the power n of the original dose is left: 50% after one, 25% after two, 12.5% after three, and so on. Enter a half-life and a time elapsed and the calculator returns the exact amount and percentage remaining.
How long until a compound is fully cleared?
Clearance is asymptotic — it never reaches exactly zero — but a compound is about 97% gone after five half-lives and roughly 99% gone after about seven. These rules of thumb are what the calculator uses for its clearance estimates.
What is steady state and when is it reached?
With repeated dosing, each dose adds to what hasn't cleared yet, so levels climb until intake balances clearance — that plateau is steady state. It's reached after roughly five half-lives of consistent dosing, the same timescale as clearance of a single dose.
What does the accumulation factor mean?
It's how much higher the steady-state peak sits compared with a single dose. Dosing far more often than the half-life produces a large accumulation factor; dosing much less often than the half-life keeps it near one, meaning little build-up.