How to Use This Calculator
Pick a peptide from the list to load its published half-life, or choose Custom and type the half-life in hours. Enter the dose in mcg and the hours since the injection. Click Calculate to see how much remains now, plus a table of what is left after each of the first 4 half-lives. Use it to see whether a compound is mostly gone by the time of the next dose.
Why Half-Life Determines Dosing Frequency
A compound is considered mostly cleared after roughly 4-5 half-lives, and reaches steady state (where the amount going in each dose roughly equals the amount being cleared) after the same number of consistent dosing intervals. A short half-life means levels swing more between doses unless dosed more frequently; a long half-life means the compound accumulates over several days before leveling off, so the first few doses look different from the steady-state pattern. Knowing which situation you’re in changes how a schedule should be read.
Peptide Half-Life Chart
This chart shows the share of a dose left after each half-life, with a 500 mcg dose as an example. It applies to any peptide, because the fraction left depends only on the number of half-lives, not on the peptide. Use the calculator above to turn hours into half-lives for the half-life you enter.
| Half-lives passed | Share of dose left | Left from 500 mcg |
|---|---|---|
| 0 | 100% | 500 mcg |
| 1 | 50% | 250 mcg |
| 2 | 25% | 125 mcg |
| 3 | 12.5% | 62.5 mcg |
| 4 | 6.25% | 31.25 mcg |
| 5 | 3.125% | 15.625 mcg |
Building This Into a Full Schedule
Once the right interval is known, the Multi-Peptide Weekly Schedule Builder lays it out across a full week, particularly useful when running a compound with a short half-life alongside one with a longer interval. For the actual per-dose draw at that interval, the Peptide Dosage Calculator converts the target dose into an exact syringe reading.
Who Should Use This
Researchers comparing how quickly different peptides clear, for example CJC-1295 with and without DAC; anyone choosing a dosing interval that keeps levels within a target range.
What This Calculator Does
The Peptide Half-Life Calculator estimates how much of a dose is still active a given number of hours after injection. Pick a common research peptide to use its preset half-life, or enter your own, and it also lists the amount left at each of the first four half-lives.
Formula Used
Fraction remaining = 0.5 ^ (Hours elapsed ÷ Half-life in hours)Remaining (mcg) = Dose (mcg) × Fraction remainingExample Calculation
Limitations
Assumes simple first-order decay with one fixed half-life. Preset half-lives are approximate published estimates; real clearance varies with route of administration, dose and the individual.
Frequently Asked Questions
What is peptide half-life and why does it matter for dosing?
Half-life is the time required for the concentration of a compound to decrease by 50% in the body. It determines how frequently a compound must be administered to maintain stable levels. Short half-life compounds (minutes to hours) require frequent dosing; long half-life compounds (days) may only need weekly administration.
How many half-lives until a peptide is fully cleared from the body?
After 5 half-lives, approximately 97% of a compound is eliminated. After 7 half-lives, over 99% is cleared. This is the standard used to determine when a compound is considered pharmacologically inactive for research washout periods.
How do I calculate how much peptide remains after a certain time?
Use the formula: Remaining = Initial Amount × (0.5)^(time elapsed ÷ half-life). The Half-Life Calculator above automates this. Enter your starting dose, the compound's half-life, and the elapsed time to see exactly how much remains.
Does the administration route affect peptide half-life?
Yes. Subcutaneous injection produces longer effective half-lives than intravenous administration because the compound is absorbed slowly from the injection depot. Oral administration drastically shortens half-life for most peptides due to enzymatic degradation in the GI tract.