Peptide Half-Life Calculator
How long does a peptide actually stay in your system? Pick your compound, dose, and how often you take it — this free half-life calculator charts your estimated level between doses and shows how much is still there when the next one lands, how far levels stack before plateauing, and how long clearance takes.
Half-life 7 days · peaks at 36 hours
Every 7 days.
Half-life
Left at next dose
Semaglutide (Ozempic, Wegovy) · once weekly · levels plateau after ~35 days
Steady-state peak
1.97 mg
Steady-state trough
1.12 mg
Accumulation
2×
At once weekly, each dose lands before the previous one has cleared, so levels stack to about 2× a single dose before plateauing — roughly 35 days in. After the last dose it takes about 35 days to clear.
This is a modelled estimate of relative levels from published half-life and time-to-peak figures — not a measured blood concentration. Individual pharmacokinetics vary.
Half-life and time-to-peak figures come from published pharmacokinetic data. This models relative levels, not a measured blood concentration.
Never do this math twice.
The Pep AI app remembers your vials and doses, shows an interactive syringe you draw to, counts down the doses left in each vial, and reminds you when it's time. Free on iOS and Android.
How half-life actually works
Half-life is the time it takes for half of a dose to be eliminated. Three consequences follow from it, and the chart above shows all three:
1. One half-life
Half the dose is gone after 7 days. After two half-lives 25% remains, after three 12.5%.
2. What's left at the next dose
Dosing once a week means the next dose lands 7 days later, with about 50% of the previous one still present.
3. Accumulation and plateau
Those leftovers stack until intake matches elimination — about 2× a single dose, reached after roughly 35 days (five half-lives).
Worked example
Semaglutide (Ozempic, Wegovy) has a half-life of 7 days. Dosing once a week, the next dose arrives 7 days later with about 50% of the previous one still on board. Levels therefore stack to roughly 2× a single dose before plateauing, which takes about 35 days — and after a final dose it takes about the same again to clear.
Why peptide half-lives vary so wildly
Peptides span an enormous pharmacokinetic range — wider than almost any other class of compound. BPC-157 has a half-life measured in minutes, so it is essentially gone within an hour or two of injecting. Semaglutide's is about a week. That is a difference of roughly three orders of magnitude between two compounds people often run side by side in the same protocol.
This is why dosing frequency differs so much. A compound that clears in an hour has to be dosed daily (or more) just to be present at all, and it never accumulates — every dose is the same isolated rise and fall. A compound with a week-long half-life dosed weekly is still at half strength when the next shot lands, so levels stack for over a month before settling into a plateau. Same injection schedule, completely different curve.
It also explains the practical rules people repeat without knowing where they come from. "It takes about five weeks to reach steady state" and "it takes about five weeks to leave your system" are the same fact: five half-lives is ~97% of the way to the plateau on the way up, and ~97% cleared on the way down.
The Pep AI app runs this same model continuously against your real logged doses, so your estimated level updates as you actually dose rather than as a hypothetical schedule — see the peptide tracker for how it fits with the rest of a protocol.
Frequently asked questions
This calculator is provided for informational and educational purposes only and is not medical advice. Always confirm dosing with a qualified healthcare professional and double-check your own measurements before administering anything.