Tool
Tirzepatide half-life calculator
Preset to tirzepatide's approximately 5-day half-life from the FDA label. See relative level over repeated doses, the accumulation ratio, and approximately how long steady state takes - adjust the interval to anything you want to model.
Guides:tirzepatide dosage (FDA schedule)·tirzepatide overview
Your numbers
Half-life approximately 5 days, per MOUNJARO (tirzepatide) prescribing information, section 12.3 Pharmacokinetics (DailyMed, National Library of Medicine). Dosing interval below is still yours to set.
How long the level takes to fall by half. Not a dose recommendation - a physical property of the compound and the person taking it.
How often an equal dose is repeated. This tool does not suggest a schedule - it only draws what a given interval would produce.
Level over repeated doses
Accumulation ratio
1.6101x
steady-state peak ÷ one dose's own peak
~90% steady state
3
doses in, ≈398.6 h (16.61 d)
Half-life 120 h (5 d). Dosed every 168 h (7 d). Steady state (about 90%) is reached after roughly 3 doses, around 398.6 h (16.61 d) after the first dose. Accumulation ratio 1.6101x: at steady state, the peak level after each dose is about 1.6101 times one dose's own peak, and the trough between doses is about 0.6101 times it.
- Elimination rate constant (k)
- 0.0058 per hour
- Steady-state peak(right after each dose)
- 1.6101x
- Steady-state trough(right before the next dose)
- 0.6101x
- ≈97% of steady state
- 607.1 h (25.29 d)
Accumulation ratio = 1 ÷ (1 − e^(−k·τ)), where k = ln(2) ÷ half-life and τ is the dosing interval. Time to steady state depends only on half-life, not on the interval - the same reason a rule of thumb like "about 4-5 half-lives" gets taught regardless of how often a dose repeats.
Half-life preset from MOUNJARO (tirzepatide) prescribing information, section 12.3 Pharmacokinetics, DailyMed, National Library of Medicine -source. Results update in the address bar so a calculation is shareable; nothing is stored.
The actual tirzepatide dose
Half-life explains how a dose behaves once it's in the body - it says nothing about how large that dose should be. The only dosing schedule that has gone through FDA review starts at 2.5 mg once weekly for four weeks, then rises in 2.5 mg steps no sooner than every four weeks, up to a 15 mg maximum. That full schedule is on the tirzepatide dosage page, and background on the drug itself is on themain tirzepatide page. For reconstitution arithmetic (vial size, diluent, draw volume), see thetirzepatide dosage calculator.
Common questions
What is the half-life of tirzepatide?
Approximately 5 days, per the Pharmacokinetics section of the Mounjaro and Zepbound FDA prescribing information. This tool is preset to that figure so the chart below shows tirzepatide's own accumulation curve, not a generic example.
Why does tirzepatide only need once-weekly dosing?
A roughly 5-day half-life against a 7-day (once-weekly) dosing interval means each dose has mostly cleared before the next one arrives, which is why the label sets a once-weekly schedule rather than daily. The chart above plots exactly that relationship for any interval you choose.
How long does it take tirzepatide to reach steady state?
Using the standard first-order model, roughly 3.3 half-lives to reach 90% of steady state - about 16-17 days at a 5-day half-life - and around 5 half-lives (about 25 days) to reach 97%. That figure comes from the half-life alone and does not depend on the once-weekly interval.
Does the half-life differ between Mounjaro and Zepbound?
No. Mounjaro and Zepbound are the same tirzepatide molecule and injection, approved for different indications (type 2 diabetes and weight management/obstructive sleep apnoea respectively), and both labels report the same pharmacokinetic profile.
Does a compounded tirzepatide vial have the same half-life?
Half-life is a property of the tirzepatide molecule's own elimination, not of how a specific product is packaged, so it should not change based on the vial. What can differ with a compounded product is purity, concentration accuracy and stability - none of which this calculator measures.
Is this a dosing recommendation?
No. It only charts the arithmetic of first-order elimination for a half-life and interval - it never suggests a dose or a schedule. For the actual FDA-approved titration schedule, see the tirzepatide dosage page.