Peptide Half-Life Calculator: Modeling Pharmacokinetic Decay Curves

A peptide's half-life represents the time it takes for the concentration of the active compound in your body to be reduced by half. Understanding half-life decay rates is critical for designing consistent dosing cycles and preventing sudden peaks or troughs in blood levels.

Understanding Half-Life Decay Math

Subcutaneous peptides decay exponentially. The amount of remaining compound in your system over elapsed time can be projected using the exponential decay formula:

For example, if you inject a 5mg dose of a peptide with a 7-day half-life:

• Day 0 (Immediately): 5.0mg active in your system.
• Day 7: 2.5mg remaining (one half-life elapsed).
• Day 14: 1.25mg remaining (two half-lives elapsed).

The Concept of Accumulation (Steady State)

If you inject a compound repeatedly before the previous dose has fully decayed, the peptide will accumulate in your bloodstream. This accumulation continues until you reach a "steady state," where the amount of peptide injected equals the amount eliminated between doses. Steady state is typically achieved after approximately 4 to 5 half-lives.

Because accumulation occurs, taking a consistent dose over time will gradually yield higher active concentrations than a single starting injection. Keeping track of this accumulation mathematically helps you maintain stable, predictable levels.

Visualizing Blood Levels inside Pepglow

Pepglow eliminates the need for manual graphing by calculating pharmacokinetic accumulation automatically. When you log your doses, the app uses standard half-life models to project your estimated active levels on an intuitive, native dashboard chart. You can visually explore:

• Active compound curves over days or weeks.
• Projected steady-state concentration zones.
• Visual markers indicating upcoming scheduled doses.

These curves are approximate and intended for personal educational awareness only. Individual metabolism varies based on body mass, clearance, and genetics.