None of the information on this site is guaranteed to be accurate. Use at your own risk.

The formula used for calculating the rate of compound release at a given day t is:

λ * N(t)

Where λ is the decay constant equal to ln(2)/h, h being the half life of the compound given in days; and N(t) is the half-life equation given by:

N(t) = n * e^(-t/λ)

Where n is the original dose of the compound in mg and t is given in days.

Terminal Half-lives

These half-lives are approximations, and may vary slightly depending on injection site, carrier oil, and other factors.

Note: A different list of half-lives is often copy and pasted on various sites, claiming that, for example, the half-life for the propionate ester is 4.5 days and that the half-life for the enanthate ester is 10.5 days. This list is incorrect, and is the result of flawed calculations many years ago. See the "References" section for more information.

Active Dose

Injectable steroids are typically bound by esters, which comprise a portion of the steroid's weight. Because of this, 100mg of, for example, testosterone enanthate does not equate to 100mg of pure testosterone. In this case, there is only 70mg of testosterone being injected, and the remaining 30mg is the enanthate ester. This is taken into account when plotting cycles on this site, as different esters have different weights. Listed below is the percentages of the actual hormones for different steroid and ester combinations:


Behre HM, Nieschlag E. 1998 Comparative pharmacokinetics of testosterone esters. In: Nieschlag E, Behre HM, eds. Testosterone: Action, Deficiency, Substitution, ed 2. Berlin: Springer-Verlag; 329–348.

Back to site