Which TRT injection frequency should you use? daily, twice weekly, or every 3.5 days

What the three frequencies actually mean

"Daily" microdosing means seven small injections a week. "Twice weekly" (often written E3.5D — one injection every three-and-a-half days, i.e. two fixed days like Monday and Thursday) means two larger injections. "Every other day" (EOD) sits between them at roughly 3.5 injections a week. Each is just a different denominator under the same weekly numerator. Injectable testosterone esters release slowly from the oil depot and produce supraphysiological peaks within hours of an injection that fall back toward baseline over the following days (Schürmeyer & Nieschlag, 1984), so a bigger, less frequent shot swings higher and lower across the week than several small ones.

Why people choose more frequent shots: subcutaneous testosterone given on a steady schedule keeps total and free testosterone stable and well within range between injections (McFarland et al., 2017), which is the practical appeal of daily or EOD microdosing. The Endocrine Society guideline frames formulation and frequency around achieving mid-normal testosterone with attention to patient preference and treatment burden, then monitoring symptoms and labs (Bhasin et al., 2018) — it does not declare one frequency universally best. The arithmetic on this page does not decide whether any schedule is right for you; it only converts a weekly total into a per-injection draw.

Per-injection mg and units, side by side

The table below splits three common weekly totals across four frequencies, all on a 200 mg/mL vial drawn on a U-100 insulin syringe. Read it as: pick your weekly total (row group), pick your frequency (row), and the cell shows the per-shot mg and units.

Notice the weekly total never moves — only the per-shot size does. The twice-weekly draw is exactly 3.5× the daily draw, because 7 injections ÷ 2 injections = 3.5. Plug your own numbers into the Testosterone (TRT) dose calculator if your weekly total or vial strength differs.

How this is calculated

Two short steps convert any weekly total into a per-injection syringe mark:

1. Per-shot mg = weekly mg ÷ injections per week. Daily uses 7, EOD uses 3.5, twice-weekly uses 2.
2. Units = per-shot mg ÷ concentration (mg/mL) × 100. The ×100 converts mL into U-100 units (100 units = 1 mL).

On a 200 mg/mL vial the second step simplifies to "per-shot mg ÷ 2 = units", which is why 70 mg reads as 35 units. Always confirm dose and concentration are in the same mass unit (mg with mg/mL) before dividing. If your vial is 250 mg/mL instead, every unit value shrinks: the same 70 mg becomes 70 ÷ 250 × 100 = 28 units.

Worked examples

Common mistakes when switching frequency

The biggest error is changing frequency but forgetting to re-divide the dose — injecting your old twice-weekly amount seven times a week multiplies your weekly total. Always recompute per-shot mg from the weekly total whenever frequency changes. A second error is copying someone else's unit number without matching vial strength: 35 units on a 250 mg/mL vial is a different dose than 35 units on a 200 mg/mL vial.

A third is ignoring dead space — the small volume left in the needle hub — which matters more as per-shot volumes get tiny on daily microdosing. Finally, correct math is still unsafe with poor technique: use a new sterile needle and syringe for every injection, never share, and follow product storage instructions (CDC). Testosterone cypionate labels describe replacement dosing of 50 to 400 mg every two to four weeks for the long-ester depot; weekly and more-frequent splits are common in practice but should match your prescriber's plan (DailyMed).

So, which TRT injection frequency should you use?

All three schedules deliver the same weekly testosterone total — only the per-shot size changes. The formula is: weekly mg divided by injections per week equals per-shot mg, then divide by concentration and multiply by 100 for U-100 units. Daily gives the smallest, steadiest shots; twice-weekly is the most common balance of convenience and stable levels; every 3.5 days is mathematically identical to twice-weekly. Use the Testosterone (TRT) dose calculator to convert your own weekly total and vial strength into exact units for any frequency.

FAQs