Half-Life Calculator
Peptide half-life decay calculator
Plot first-order exponential decay: A(t) = A₀ × 0.5^(t/T½). Read the 50%, 25%, 10%, and 1% milestones for any peptide in the catalog.
The formula
A(t) = A₀ × 0.5(t / T½), the fraction remaining after time t equals one half raised to the number of half-lives elapsed.
Time to reach a target percentage P of the starting amount: t = T½ × log₂(100 / P). After 5 half-lives, ≈ 3.1% remains, the standard "effectively cleared" benchmark.
Worked example, Retatrutide, T½ ≈ 6 days
- 50% remaining at 1 × T½ = 6 days
- 25% remaining at 2 × T½ = 12 days
- 12.5% remaining at 3 × T½ = 18 days
- 10% remaining at ≈ 19.9 days (T½ × log₂(10) = 6 × 3.32)
- 3.1% remaining at 5 × T½ = 30 days ("effectively cleared")
- 1% remaining at ≈ 39.9 days (T½ × log₂(100) = 6 × 6.64)
Common reference half-lives
- Semaglutide
- ≈ 7 days · 50% at 7 d · 1% at ≈ 47 d
- Retatrutide
- ≈ 6 days · 50% at 6 d · 1% at ≈ 40 d
- Tirzepatide
- ≈ 5 days · 50% at 5 d · 1% at ≈ 33 d
- BPC-157 (IV, rats)
- ≈ 15 minutes · 50% at 15 min · 1% at ≈ 1.7 h
- Ipamorelin
- ≈ 2 hours · 50% at 2 h · 1% at ≈ 13 h
- Tesamorelin
- ≈ 26 minutes · 50% at 26 min · 1% at ≈ 2.9 h
What this tool does not do
- Does not model absorption (Bateman / two-compartment PK). Input is starting blood-level amount; t = 0 is peak.
- Does not model individual variability, published half-lives are population means.
- Does not compute steady-state accumulation for repeated dosing. SS plateau ≈ D / (1 − 0.5^(τ/T½)) where τ is dose interval.
- Does not extrapolate beyond what the published half-life supports.
Arithmetic only. This view does not suggest, recommend, or validate any dose, schedule, or washout window. Consult a qualified clinician before any human use.
Open the interactive PeptideHelper.org half-life calculator to pick a peptide or enter a custom T½ and read the decay curve directly.
Frequently asked questions
How long until a peptide is effectively cleared from the body?
About 5 half-lives. After 5 × T½, roughly 3.1% of the starting amount remains; after 7 × T½, under 1%; after 10 × T½, under 0.1%. For a peptide with a 7-day half-life like semaglutide, that is roughly 35 days for the 5-half-life mark.
What is the formula for peptide half-life decay?
Single-compartment first-order decay: A(t) = A₀ × 0.5^(t / T½), where A(t) is the amount remaining at time t, A₀ is the starting amount, and T½ is the half-life. Equivalently, A(t) = A₀ × e^(−t × ln(2) / T½).
How do I calculate when a peptide reaches a specific remaining percentage?
Solve for t: t = T½ × log₂(100 / P), where P is the target percentage. For P = 10% with a 6-day half-life: t = 6 × log₂(10) ≈ 6 × 3.32 ≈ 19.9 days.
Does this calculator account for absorption or steady-state accumulation?
No. This is single-compartment first-order decay only. It assumes t = 0 is peak blood level (no absorption modeling) and a single dose (no recurring-dose accumulation). Steady-state plateau for recurring dosing every τ hours is approximated by D / (1 − 0.5^(τ / T½)).
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