# Peptide Half-Life Calculator — active levels & steady state

Source: https://pepvault.app/tools/peptide-half-life-calculator

Last updated: 2026-09-29

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# Peptide half-life & active-level calculator

See how a compound accumulates to steady state at your dose and schedule — the estimated active amount over time, plus peak and trough once it levels off.

Your schedule

Example numbers

In week 4, an estimated peak of 3.84 mg and trough of 1.93 mg. About 5 weeks to steady state.

Estimated level over 28 days

- **Week 4 peak:** 3.84 mg
- **Week 4 trough:** 1.93 mg
- **To steady state:** ~5 wk

Estimate from a published/typical half-life (one-compartment model), not a measurement. Real levels vary with absorption, body weight, and the specific compound. Use it to understand the *shape* of accumulation, not as a target.

## What half-life means for your protocol

A compound's half-life is how long it takes for half of it to clear. Each dose stacks on what's left of the previous ones, so levels climb until what you take each interval equals what you clear — that plateau is **steady state**, reached after roughly five half-lives.

This is why a long-half-life GLP-1 like semaglutide or retatrutide *feels* different at week 4 than week 1 — it's still building. Short-half-life peptides clear between doses, so their curve spikes and falls rather than plateauing high.

Example: semaglutide, with a half-life of about 7 days, taken at 2 mg once weekly reaches steady state in about 5 weeks. In week 4 its estimated peak is 3.84 mg and its trough 1.93 mg.

## Used most with

- [Semaglutide](https://pepvault.app/peptides/semaglutide)
- [Tirzepatide](https://pepvault.app/peptides/tirzepatide)
- [Retatrutide](https://pepvault.app/peptides/retatrutide)
- [MK-677](https://pepvault.app/peptides/mk-677)
- [BPC-157](https://pepvault.app/peptides/bpc-157)
- [Ipamorelin](https://pepvault.app/peptides/ipamorelin)
- [Hexarelin](https://pepvault.app/peptides/hexarelin)
- [Tesamorelin](https://pepvault.app/peptides/tesamorelin)
- [CJC-1295 no DAC](https://pepvault.app/peptides/cjc-1295-no-dac)
- [Sermorelin](https://pepvault.app/peptides/sermorelin)

PepVault for iPhone

## Track this in PepVault

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## More free tools

- [Reconstitution calculator](https://pepvault.app/tools/reconstitution-calculator)
- [Reverse reconstitution](https://pepvault.app/tools/reverse-reconstitution-calculator)
- [GLP-1 titration planner](https://pepvault.app/tools/glp1-titration-calculator)
- [Dose & unit converter](https://pepvault.app/tools/peptide-dosage-calculator)
- [How long will my vial last?](https://pepvault.app/tools/how-long-will-my-vial-last)
- [Missed a GLP-1 dose?](https://pepvault.app/tools/missed-glp1-dose)
- [Is my mixed vial still good?](https://pepvault.app/tools/reconstituted-peptide-expiry)
- [Protein on a GLP-1](https://pepvault.app/tools/glp1-protein-calculator)
- [GLP-1 weight loss by week](https://pepvault.app/tools/glp1-weight-loss-by-week)
- [Peptide reference library](https://pepvault.app/peptides)

Choosing a tracker app? [Compare peptide tracker apps](https://pepvault.app/best-peptide-tracker-apps) · [Track what’s left in your vials](https://pepvault.app/peptide-vial-tracker-app)

PepVault is a research and tracking resource, not medical advice. Ranges are what studies used, never a dose for you. Brand names are trademarks of their owners; PepVault is independent of them.

For educational and tracking purposes only — not medical advice. Always verify calculations and consult a qualified clinician before changing any protocol.

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