What Is Testosterone Cypionate? Half-Life, mg/mL Dosing & Tracking

Quick answer

Testosterone cypionate is testosterone attached to the cypionate ester, an oil-soluble chain that slows its release so it can be injected roughly weekly instead of daily. Its ester half-life is around 7–8 days. On a label it is sold by concentration (mg/mL), not total mg — the single most common source of dosing errors. Educational only; TRT dosing is set by your prescriber.

What testosterone cypionate is and how it works

Testosterone cypionate is plain testosterone with a cypionate ester bonded to it. The ester is the entire point: it is an oil-soluble carbon chain that makes the molecule sit in a depot at the injection site and release slowly into the blood, where enzymes cleave the ester off and free testosterone does its job.

Crucially, the ester does not change what testosterone does or how strong it is — it only changes timing. “Cypionate vs enanthate” potency debates are largely mythology; once the ester is cleaved, your body sees identical free testosterone. What the ester buys you is a practical, roughly-weekly injection schedule instead of the near-daily one bare testosterone would require.

One consequence of the ester’s weight: about 70% of the milligrams in testosterone cypionate are testosterone; the rest is the ester. So 100 mg of cypionate delivers roughly 70 mg of actual hormone.

Dosing math & the mg/mL trap

TRT testosterone is labeled by concentration — milligrams per milliliter — which trips up anyone coming from peptides, where a vial is labeled by total mg. A “200 mg/mL” vial is a rate, not a total: a 10 mL vial at 200 mg/mL holds 2,000 mg, not 200 mg.

The arithmetic to turn a prescribed dose into a volume is one line: volume (mL) = dose (mg) ÷ concentration (mg/mL). So 100 mg from a 200 mg/mL vial is 0.5 mL — 50 units on a U-100 insulin syringe. Weekly protocols are often split (e.g., Monday/Thursday) to steady levels; divide the weekly mg by the number of shots first, then apply the formula.

Dose	100 mg/mL	200 mg/mL	250 mg/mL
50 mg	0.50 mL (50u)	0.25 mL (25u)	0.20 mL (20u)
100 mg	1.00 mL (100u)	0.50 mL (50u)	0.40 mL (40u)
150 mg	1.50 mL (150u)	0.75 mL (75u)	0.60 mL (60u)
200 mg	2.00 mL (200u)	1.00 mL (100u)	0.80 mL (80u)

Volume to draw for common per-injection doses at three concentrations (U-100 syringe units in parentheses). We wrote a whole piece on this trap — linked below — and the HRT tab of the calculator does it for you.

Half-life & what it means for frequency

The cypionate ester’s terminal half-life is on the order of 7–8 days (references cluster around 6.9 days). That is what sets the injection rhythm: long enough that once-weekly keeps testosterone in a usable range, short enough that a single weekly bolus still peaks and troughs noticeably across the week.

That swing is why many people — and many prescribers — split the weekly dose into two or more smaller injections. Same weekly total, flatter curve: less of a peak a day or two after the shot, less of a dip before the next one. You can see the exact shape for any dose and frequency in the blood-level simulator; a representative 200 mg/week comes out around a ~1,230 ng/dL peak and ~700 ng/dL trough at steady state.

What to track on TRT

TRT is a monitored therapy, and the things worth tracking are the labs your prescriber follows: total and free testosterone (ideally drawn at trough, right before your next injection, so the number is comparable week to week), estradiol, hematocrit (testosterone can thicken the blood), and a lipid panel. Symptoms — energy, libido, mood, sleep — are the other half of the picture.

The recurring theme is timing: a testosterone level only means something if you know where in the week it was drawn. A number without its trough-or-peak context is nearly uninterpretable — exactly the kind of thing that is easy to lose and worth logging.

Frequently asked questions

Is testosterone cypionate the same as enanthate?

Effectively yes, for practical purposes. Both are long esters of the same testosterone molecule with near-identical release; once the ester is cleaved your body sees identical free testosterone. Cypionate’s half-life (~6.9–8 days) is a touch longer than enanthate’s, but potency debates between them are largely myth.

What is the half-life of testosterone cypionate?

The cypionate ester’s terminal half-life is roughly 7–8 days (commonly cited near 6.9 days). That drives the weekly injection rhythm and the peak-to-trough swing that leads many to split the weekly dose.

Does a 200 mg/mL vial contain 200 mg?

Only if it happens to be exactly 1 mL. Concentration (mg/mL) is a rate, not a total — a 10 mL vial at 200 mg/mL holds 2,000 mg. Total mg = concentration × vial volume.

How do you convert a testosterone dose to mL?

Volume (mL) = dose (mg) ÷ concentration (mg/mL). For example, 100 mg from a 200 mg/mL vial is 0.5 mL, or 50 units on a U-100 syringe. The HRT tab of the calculator does it for any concentration.

This is educational information, not medical advice. Doses and protocols above reflect published references and community practice — protocol decisions belong with your prescribing physician. Generic names used throughout. How this reference is built & how the AI is tested →

What Is Testosterone Cypionate? Half-Life, Dosing Math & How to Track It