Tools · TRT
Testosterone ester half-life visualizer
By An NayalLast reviewed
Pick an ester, a dose and how often you inject, and see the shape it makes: how levels build over the first weeks toward a steady state, and how much they swing between shots. This draws the shape from the ester's half-life. It is a teaching picture, not a blood level.
Steady-state peak
220rel.
Steady-state trough
120rel.
Peak-to-trough swing
1.83x
Higher = bigger ups and downs between shots.
Relative serum level over 10 weeks
Illustrative shape only, in relative units. Not a predicted blood level.
Read this before you read the chart
This is an illustrative teaching model, not a validated pharmacokinetic simulator and not a predicted blood level. It draws a relative curve by decaying each injection from the ester's published half-life and adding them up. It ignores absorption time, individual clearance, injection site, and everything an assay would actually measure, so the numbers are unitless and relative, not ng/dL. Use it to see the shape - how levels stack up and swing between shots - not to plan a protocol. It is math only, not medical advice. Always verify with a licensed provider. Testosterone is a controlled substance in many places.
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Worked example
The visualizer opens on testosterone cypionate (half-life about 8 days), 100 mg per injection, once a week. All numbers below are in the tool's relative units, not ng/dL.
- Fraction left after one interval: r = 0.57/8 = 0.545. So a week after a shot, about 55% of it is still counted.
- The first shot peaks at 100. The second lands on the 54.5 left over, so it peaks at 154.5. By the fifth shot (day 28) the peak is 209.
- Steady-state peak: 100 / (1 - 0.545) = 220.
- Steady-state trough, just before the next shot: 220 x 0.545 = 120.
- Peak-to-trough swing: 220 / 120 = 1.83x.
Keep the dose and switch the interval to every 3.5 days. The peak rises to 382, the trough to 282, and the swing narrows to 1.35x. Now go back to weekly and pick enanthate (4.5 days): the peak is 152, the trough 52, and the swing grows to 2.94x.
How the model works, and what it is not
Each injection is treated as an instant input that fades by simple first-order decay from the ester's published half-life. After one half-life, half remains; after two, a quarter. The curve at any day is the sum of every past injection still decaying:
level(t) = sum of dose x 0.5^((t - t_injection) / half-life)
Injections start on day 0 and repeat at your interval across the 10-week chart, sampled at 600 points so the sawtooth shows. The steady-state numbers come straight from the geometric series, not from reading the chart:
r = 0.5^(interval / half-life)
peak = dose / (1 - r); trough = peak x r; swing = 1 / r
The dashed lines on the chart mark that peak and trough, and the chart height is set to 1.08 times the peak. Peak and trough show as whole numbers and the swing to two decimals. The model reaches its plateau after about four to five half-lives. A shorter half-life means bigger swings at the same interval. If the dose is empty, zero or not a number, no curve is drawn.
What this is not: it is not a predicted blood level and not a validated pharmacokinetic simulator. It ignores absorption time, how fast your body clears the drug, the injection site, and assay differences, so the numbers are relative and unitless, not ng/dL. Read it for the shape, never as a protocol.
Questions people ask
What half-lives does the calculator use for each ester?
About 8 days for testosterone cypionate, 4.5 days for enanthate and 1 day for propionate, taken from each compound's reference card. The dropdown shows the half-life next to each name.
How long until levels reach steady state in this model?
About four to five half-lives. With cypionate's 8-day half-life and weekly shots, the peak after the fifth shot (day 28) is 209, about 95% of the steady-state peak of 220.
Why does a shorter half-life give bigger swings?
The swing ratio is 2 to the power of (interval / half-life). At a weekly interval that is 1.83x for cypionate (8 days), 2.94x for enanthate (4.5 days) and 128x for propionate (1 day).
Are the numbers blood levels in ng/dL?
No. They are relative, dose-equivalent units, labeled rel. The model ignores absorption time, individual clearance, injection site and assays, so it shows the shape of the curve, not a predicted lab result.
Pepteca is for education and information only. It does not provide medical advice, diagnosis, or treatment, and its calculators perform unit math only. Always verify with a licensed provider before starting, changing, or stopping any protocol. Many peptides are not approved for human use and may be regulated differently where you live.