Testosterone Enanthate Half-Life Calculator
The apparent serum half-life of testosterone enanthate after a shot is about 6.9 days. This calculator visualizes serum levels under any dose and frequency, including the difference between weekly and twice-weekly protocols.
Peak Level
219 mg
Half-Life
6.9 days
Steady State
~5 weeks
Full Clearance
~35 days
Keep your compounds in Regimen and see your levels between doses.
Get RegimenFor educational and research purposes only. This calculator provides estimates based on standard formulas.
Always verify calculations with your healthcare provider before use. We assume no liability for dosing errors, adverse events, or outcomes resulting from use of this tool.
Worked example: 200 mg/week, weekly vs twice weekly
Testosterone enanthate is an oil-based intramuscular or subcutaneous testosterone ester. The apparent serum half-life after a shot is about 6.9 days, governed by release from the oil depot rather than clearance of free testosterone (flip-flop kinetics). That release-limited rate is short enough that injection frequency still has a meaningful effect on the peak-to-trough variance you experience week to week.
Take a 200 mg per week protocol. Injected as a single weekly dose (200 mg on Monday), the curve climbs into a peak around day 2 to 3, then declines steadily across the following 4 to 5 days. The trough just before the next injection sits at roughly 55 to 60 percent of the peak. That swing is what some users experience as a "low ebb" in the second half of the week.
Split the same 200 mg into two 100 mg injections (Monday and Thursday), and the curve compresses meaningfully. Peaks are lower, troughs are higher, and the trough-to-peak ratio rises to roughly 75 to 80 percent. Lower peaks mean less aromatization to estradiol from supraphysiological spikes. Higher troughs mean less symptomatic variance. This is why most modern TRT protocols default to twice-weekly injection at minimum, and some go to every-other-day or daily microdose protocols for the flattest possible levels.
Test E vs test C: are they actually different?
Practically, no. Testosterone enanthate and cypionate are near-identical esters, and both carry an apparent serum half-life of about 6.9 days, so the curve you see after a shot behaves the same way. You will sometimes see enanthate quoted around 4.5 days and cypionate around 8 days, but those older textbook figures imply a gap that does not hold up: the two are dosed interchangeably and clear the blood on essentially the same timeline. We anchor both to the rigorous measured pharmacokinetic data, which lands at about 6.9 days. So the same twice-weekly-vs-weekly math applies to either ester.
Frequently asked questions
What is testosterone enanthate's half-life?
The apparent serum half-life of testosterone enanthate after a shot is about 6.9 days, based on rigorous measured pharmacokinetic data. This describes how fast the curve in your blood declines after injection, since the rate-limiting step is release from the oil depot rather than clearance of free testosterone.
When does test E reach steady state on weekly injections?
Roughly 4 to 5 half-lives, which is about 4 to 5 weeks of consistent weekly injecting at a fixed dose. Lab trough values are typically pulled at the 4 to 6 week mark to confirm the dose.
Should I split test E into twice-weekly injections?
Yes for most TRT protocols. With an apparent half-life around 6.9 days, weekly dosing still produces a noticeable peak-to-trough swing. Twice-weekly (every 3 to 4 days) injections cut that swing meaningfully, which generally improves symptom stability and lowers estradiol conversion from supraphysiological peaks.
Test E vs test C: are they actually different?
Practically, no. Testosterone enanthate and cypionate are near-identical esters, and both carry an apparent serum half-life of about 6.9 days, so the curve you see after a shot behaves the same way. You will sometimes see enanthate quoted around 4.5 days and cypionate around 8 days, but those older textbook figures imply a gap that does not hold up: the two are dosed interchangeably and clear the blood on essentially the same timeline. We anchor both to the rigorous measured pharmacokinetic data, which lands at about 6.9 days. So the same twice-weekly-vs-weekly math applies to either ester.
How long does test E stay in your system after stopping?
Clinically meaningful exposure persists for about 4 to 5 weeks after a final injection (4 to 5 half-lives). HPG axis recovery, which is a separate question from clearance, typically takes longer and is the more relevant timeline for anyone planning to discontinue.
For dose math, open the TRT injection calculator. For a deeper dive into daily microdosing math, read the daily TRT insulin syringe dose guide.
Track your real test E levels, not just the model
Regimen logs each injection and builds your personal PK curve. Pair it with lab uploads to compare modeled vs measured.
- Personalized PK curves
- Twice-weekly injection reminders
- Symptom and lab correlation
- Private, secure health data
