Semaglutide Half-Life Calculator
Semaglutide has a half-life of about one week — the longest of the common GLP-1s. This free calculator charts what that means for a weekly shot: how much is still in you when the next dose lands, how many weeks levels keep climbing before they plateau, and how long semaglutide takes to leave your system.
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
0.99 mg
Steady-state trough
0.56 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.
Based on a published semaglutide half-life of ~168 hours. 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.
What a 7-day half-life means in practice
Semaglutide's roughly 168-hour half-life is why it's a once-weekly shot, and why the first month feels different from the sixth. Three consequences:
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 semaglutide takes about five weeks to settle
Because the half-life and the dosing interval are both about seven days, semaglutide lands in an unusually clean case: exactly half of each dose is still present when the next one arrives. That means levels stack to roughly twice a single dose before they plateau — and it takes about five half-lives, or five weeks, to get there.
This has two practical consequences people notice. First, the effects of a dose change keep developing for weeks after the change; you are not at the full level of a new dose the week you start it. Second, the same arithmetic runs in reverse when you stop — semaglutide is still measurably present for about five weeks after your last shot, which is why side effects can take a while to fade and why clinicians plan washout periods around it.
It also explains why a missed dose is less dramatic with semaglutide than with a short-half-life compound. With half of the previous dose still on board, one skipped week dips your level rather than dropping it to nothing.
Pep AI runs this model against your actual logged shots, so your level curve reflects the doses you really took — including the late ones — rather than a perfect schedule. The semaglutide tracker covers shot day, titration, and side effects alongside it.
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.