Peptide Half-Life & Decay Calculator
Calculate active remaining compound levels over time, half-lives elapsed, clearance percentages, and elimination timelines.
Elimination Curve Breakdown
| Time since dose | Percentage remaining |
|---|---|
| 0.0d | 100.0% |
| 0.5d | 70.7% |
| 1.0d | 50.0% |
| 1.5d | 35.4% |
| 2.0d | 25.0% |
| 2.5d | 17.7% |
| 3.0d | 12.5% |
| 3.5d | 8.8% |
| 4.0d | 6.3% |
| 4.5d | 4.4% |
| 5.0d | 3.1% |
Pharmacokinetics & First-Order Elimination Math
Written out so you can check it by hand. The app runs this exact function, not a second implementation that drifts.
Peptide clearance typically follows first-order elimination kinetics, where a constant fraction of compound is cleared per unit of time.
1. Exponential Decay Formula: N(t) = N₀ × (0.5)^(t ÷ t½), where N₀ is the initial dose, t is elapsed time, and t½ is the elimination half-life.
2. Half-Lives Elapsed: Half-Lives = Elapsed Time ÷ Half-Life Duration. After 2 half-lives, 25% remains (75% eliminated). After 3 half-lives, 12.5% remains.
3. Clearance Thresholds: 50% elimination occurs at 1 half-life; 90% elimination occurs at ~3.32 half-lives; 99% elimination occurs at ~6.64 half-lives.
- What is elimination half-life (t½)?
- Elimination half-life is the duration of time required for the active concentration of a compound in the body to decline by exactly 50% through metabolic clearance and excretion.
- How long does it take for a peptide to be fully eliminated?
- In pharmacology, a compound is considered functionally cleared (over 98.4% eliminated, i.e. 1 − 0.5⁶) after 6 half-lives. For example, a peptide with a 4-hour half-life clears in approximately 24 hours. Source: Hallare & Gerriets, Elimination Half-Life of Drugs, StatPearls (NCBI NBK554498).
- What is steady-state accumulation?
- When a compound is administered on a repeating schedule faster than it clears, blood levels accumulate over time until input balances elimination. Steady state is achieved after roughly 4 to 5 half-lives. Source: Hallare & Gerriets, Elimination Half-Life of Drugs, StatPearls (NCBI NBK554498).
- What are the most common half-life reasoning mistakes?
- Reading half-life as "time until gone": after one half-life 50% remains, and full clearance takes about six. Assuming effect tracks blood level one-to-one, which many compounds do not. And ignoring accumulation: dosing more often than the compound clears raises the steady-state level well above what a single dose produces, which is exactly what the accumulation view here models.
- Why do half-lives vary between subcutaneous and intravenous administration?
- Subcutaneous administration creates a depot effect where the compound slowly absorbs into capillaries over hours, extending the apparent terminal half-life compared to rapid intravenous injection.
The number is right. Now keep the record.
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