OptiPin
Half-life calculator
See how much testosterone, anabolics, peptides or GLP-1s are actually in your system over time, in mg or mcg, at steady state or from a single dose, using published half-life and time-to-peak values for 65 compounds.
This web tool uses one shared one-compartment (Bateman) curve to illustrate timing. The OptiPin app runs more advanced, compound-specific models and personalizes them to you:
- Testosterone uses a saturation-then-decay absorption model calibrated per ester, layered on your endogenous baseline – then recalibrated to your bloodwork and converted to a free-testosterone estimate shown against reference ranges.
- Estradiol esters use a separate absorption-scaled model tuned to each formulation, also calibrated to your labs.
- Peptides, GLP-1s, and anabolics use compound-specific pharmacokinetics with evidence-quality flags, so weakly-characterized compounds are marked as estimates.
This page estimates how much compound is in your system in mg or mcg. The app goes further and outputs personalized blood levels in clinical units, calibrated to your own bloodwork.
See your levels in OptiPin
OptiPin forecasts testosterone, estrogen, DHT, and GLP-1 levels from your actual logged doses and calibrates to your bloodwork – all on-device, no cloud required.
Download on the App StoreWhy half-life matters more than dose size
It sets your injection frequency. A compound is dosed relative to its half-life, not its strength. Testosterone propionate (t½ ~1 day) needs every-other-day injections to stay stable; cypionate (t½ ~3.8 days) is far steadier split across two injections a week. Inject a short ester weekly and you get a peak-and-crash curve regardless of how much you use.
It tells you when bloodwork is meaningful. Testing before steady state measures a level that is still climbing. For testosterone cypionate that means waiting about 17 days after starting or changing a dose; for testosterone undecanoate in castor oil, closer to five months. Draw earlier and you will under-read your own protocol.
It sets the washout after stopping. The same arithmetic runs backwards. Five half-lives is the practical clearance figure – days for an oral like Anavar, over a month for a long-ester injectable, and longer still for undecanoate. This is what determines how long a change takes to show up in how you feel.
It explains accumulation. If you dose more often than your compound clears, each dose lands on top of the residue of the last. That accumulation is why steady-state levels sit well above the peak of a first dose, and it is the part people most often underestimate. The calculator above opens on steady state, so the gap for your own interval is the first thing it shows you.
Frequently asked questions
What is the half-life of testosterone cypionate?
About 3.8 days, with a peak around 1.8 days after an intramuscular injection. That puts steady state at about 17 days of regular dosing and full clearance at about 19 days after the last shot. The figure comes from the one published population PK model for the ester (Bi 2018), so it sits below the 8 days stated on the Depo-Testosterone label. Enanthate is close at ~4.5 days; propionate is far shorter at ~1 day.
How do I calculate a testosterone half-life?
You do not calculate the half-life itself – it is a measured property of the ester, taken from published pharmacokinetic studies. What you calculate from it is time to steady state (about 4.3 half-lives) and time to clear (about 5). Select your ester above and the calculator plots the curve from its published half-life and time to peak.
What is the half-life of Anavar?
Oxandrolone sits at roughly 10 hours, per the FDA Oxandrin label, which is why it is dosed daily rather than weekly. It reaches steady state in just under two days and clears a little over two days after the last dose. Most oral steroids are in this range, and that gap is the main practical difference between orals and injectables.
Do peptides have half-lives too?
Yes, usually far shorter than steroid esters. BPC-157 is around 3.6 hours and HGH about 4 hours. The GLP-1 agonists are the exception at roughly 5–7 days for tirzepatide, semaglutide and retatrutide, which is why they are dosed weekly while most repair peptides are dosed daily or more often.
Should I enter my weekly total or my per-injection dose?
Either. The Per dose / Per week switch above the dose field lets you type whichever number you actually think in. Most TRT protocols are written as a weekly total (say 200 mg/week split twice weekly), while peptides are usually written per injection. Switch between them and the calculator converts the figure for you, so 200 mg per week twice weekly and 100 mg per dose plot the identical curve.
How long until a compound reaches steady state?
With regular dosing, blood levels reach about 94% of steady state after 4 half-lives and ~97% after 5. For testosterone cypionate that is about 17 days; for a short ester like propionate, a few days.
What does the curve represent?
The estimated amount of compound still in your system over time, in the same unit as your dose, using a one-compartment pharmacokinetic model (Bateman function) with the compound's published half-life and time to peak. Because each dose lands on the residue of the last, steady-state levels sit well above a single dose peak. It is an amount in the body, not a blood concentration in ng/dL, and it is an educational model rather than a personalized prediction.
How long until a compound fully clears after stopping?
After the last dose, a compound is effectively cleared after about 5 half-lives (~97% eliminated). For testosterone cypionate that is about 19 days; for propionate, about five days. Long esters like undecanoate take months.
How to read this
Half-life is the time for blood levels of a single dose to fall by half. A longer half-life means slower clearance and more accumulation with repeat dosing.
Steady state is reached after about 4–5 half-lives of regular dosing – that's when the amount you take each interval roughly equals the amount cleared. Levels then oscillate between a peak and trough. Shorter intervals relative to half-life produce a flatter curve.
Full clearance is the mirror image: after your last dose, a compound is effectively gone after about 5 half-lives (~97% eliminated). For a long ester this can be over a month; for a short one, days.