Testosterone half-life calculator: cypionate and enanthate
Short answer: Testosterone cypionate is usually given a half-life of around 8 days and enanthate around 4 to 5 days after an intramuscular injection, although published figures vary. Choose your ester, enter your injection interval, and the chart shows an illustrative estimate of how levels rise and fall between injections and how that changes if injections are split more often.
Why the schedule changes the curve
With a long gap between injections, the level peaks after each one and falls further before the next, which some people notice as a dip in energy or mood near the end of the cycle. Splitting the same weekly amount into smaller, more frequent injections gives a flatter line with smaller swings. Try changing the interval above from 7 days to 3.5 days and compare the "left before each dose" figure. Changing your schedule is a decision for your clinician, often guided by blood tests.
Half-life figures used
- Testosterone cypionate: about 8 days (192 hours) in the model.
- Testosterone enanthate: about 4.5 days (108 hours) in the model.
These are typical published estimates for intramuscular oil injections. Sources quote different values, and the release from an oil depot is not a simple one-step process. Edit the half-life box if your clinic uses a different figure.
Blood tests and timing
Clinics often ask for blood to be taken at a particular point in the cycle, commonly just before an injection. Knowing exactly when your last injection was makes those results much easier to read.
See your real curve, from your real doses
This page assumes a perfectly regular schedule. Real life has late doses, skipped weeks and dose changes. PepLevel builds the same kind of illustrative estimate from the doses you actually logged, with a marker for right now, for any compound with a half-life. Most people use it to make sense of hunger coming back, side effects on certain days, or the build-up after a dose change. The basic curve is free, and Pro can overlay your weight and side effects on it. It is always labelled as an estimate, never a blood test.
Common questions
What is the half-life of testosterone cypionate?
Published estimates are commonly around 8 days after an intramuscular injection, though figures vary between sources and individuals.
How long does a testosterone injection last?
Levels rise over the first days after an injection and then fall gradually. With cypionate or enanthate most of it has cleared after about 5 half-lives, but how long the effect lasts for you depends on your dose, schedule and body. Ask your clinician.
Is injecting twice a week more stable than once a week?
In the model, splitting the same weekly amount into two injections gives smaller peaks and dips. Whether that suits you is for your clinician to decide.
PepLevel does this from your own doses
Saved vials, planned doses in mL, and a level curve built from what you actually logged. Coming soon to the App Store.
Get PepLevelMedical disclaimer: this tool does arithmetic and illustrative estimates only. It is not medical advice, does not recommend any dose and is not a substitute for your prescriber, pharmacist or the product information. PepLevel is a logging and reminder tool only.