Tirzepatide Half-Life Calculator
Tirzepatide has a reported half-life of about five days — 120 hours. See how much of your last injection is left, when it's essentially gone and where a weekly protocol plateaus.
Fill in the vial, the water and the dose to see the result.
Personal journal. Not medical advice.
The curve of your protocol
Each step up is an injection; the light band is steady state, where what goes in matches what goes out.
How the tirzepatide half-life calculation works
A 120-hour half-life with injections every 168: less is left between one dose and the next than with semaglutide. The three calculations below use those values.
Half every cycle
A half-life is how long your body takes to clear half of what's circulating. After two, a quarter is left; after three, an eighth.
remaining = dose × 0.5^(time ÷ half-life)5 mg × 0.5^(72 ÷ 120) = 3.299 mgFive is the magic number
After five half-lives about 3% is left — in practice, it's gone. It's the same number for reaching steady state when you keep injecting.
time to clear = 5 × half-life5 × 120 h = 600 h (25 days)That's why it stacks
Inject again before the last one clears and the leftover adds up. The build-up settles at a predictable plateau — that's what the curve shows.
accumulation = 1 ÷ (1 − 0.5^(interval ÷ half-life))1 ÷ (1 − 0.5^(168 ÷ 120)) = 1.61×The two calculations that matter
remaining = dose × 0.5^(t ÷ t½) · peak = dose × accumulationThe first answers “how much is still in me”; the second, “where does that settle if I keep injecting”. Keep time and half-life in the same unit.
A 5 mg dose with a 5 days half-life leaves 3.299 mg in your system after 3 days. Injecting every 7 days, the steady-state peak reaches 8.05 mg — 1.61× a single injection — and the compound is essentially gone in 25 days.
The conversions people look up
How much tirzepatide is left after 7 days?
About 38%, against 49% for semaglutide — the shorter half-life lets the curve fall further.
And after 3 days?
About 66%. Two thirds of the dose is still there when the week hits its midpoint.
And after 14 days?
About 14%, against 24% for semaglutide over the same stretch.
How much is left after 5 days?
Half, by definition: five days is exactly one 120-hour half-life.
Half by half
How much of one injection is left after each half-life.
| Half-lives | Time | Remaining |
|---|---|---|
| 1 | 5 days | 50% |
| 2 | 10 days | 25% |
| 3 | 15 days | 12.5% |
| 4 | 20 days | 6.25% |
| 5 | 25 days | 3.13% |
Five days, injected every seven
Tirzepatide's reported half-life is around 120 hours, about five days. With a standard seven-day interval, each injection arrives when a little over a third of the previous one is left — enough margin for the weekly schedule to work, but less accumulation than semaglutide.
In practice the steady-state peak sits around 1.6× that of a single injection, against roughly 2× for semaglutide. And the plateau arrives sooner: five half-lives of 120 hours is about 25 days, a bit over three and a half weeks.
That's why tirzepatide titration usually waits four weeks per step — long enough for steady state to form before judging how you responded to that dose. This model only describes the amount in your system; whether to step up is a clinical decision.
Do this math once. Once.
In PepPro you enter the vial and the water a single time. From then on the app works out every injection on its own, shows the units on a visual syringe, reminds you at the right moment and keeps the whole history.
- Your reconstitution stays saved per vial
- Exact units on a visual syringe before you inject
- Reminders, titration and injection-site rotation
- Full history of doses, weight and how you feel
Exact units on a visual syringe before you inject
Good question. We've got answers.
Didn't find what you were after? Email us at contato@upsidecompany.com.br.
About 120 hours, roughly five days. Shorter than semaglutide's (~165 h), but long enough to comfortably support weekly injection.
By the five-half-lives ruler, about 25 days until roughly 3% of a dose remains. Five days after injecting, half is still there; after ten days, a quarter.
Around 25 days — three and a half to four weeks — on weekly injections. That's why giving each titration step four weeks before judging the effect makes sense.
Yes, because its half-life is shorter relative to the seven-day interval. The steady-state peak sits around 1.6× a single injection, against roughly 2× for semaglutide. You can compare the two by changing the half-life field above.
The calculator shows what happens to the amount in your system if you space it out: at a 336-hour interval, almost nothing accumulates and the trough drops much lower. Whether that's appropriate is your healthcare professional's call — the studied schedule is weekly.
Yes — that's exactly what PepPro is for. Enter the vial and the reconstitution once and the app takes over: it works out every injection, shows the units on a visual syringe, reminds you when it's time and keeps the history of doses, weight and how you feel.
No. PepPro is a personal journal and this calculator is an educational tool. Nothing here replaces a qualified healthcare professional — they're the one who decides whether, how much and how you should use any compound.
Same math, presets ready
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Personal journal. Not medical advice.
Disclaimer
This calculator is 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.