Testosterone (TRT) microdosing math

Last updated: June 2026 · Reviewed June 2026 · Built by the InjectBuddy team

How do you microdose TRT on 100mg/week? EOD split, units, and worked examples

Q: Why is EOD 3.5 injections instead of 4?

Dosing every 2 days across a 7-day week averages 7 divided by 2, which is 3.5 doses. Over a 14-day fortnight you inject 7 times, which is exactly 3.5 per week.

A 100 mg/week testosterone total split every-other-day is 28.57 mg per injection (100 ÷ 3.5, as EOD averages 3.5 shots per week). That lands at about 14.3 units on a U-100 syringe at 200 mg/mL, or 28.6 units at 100 mg/mL. This guide walks through the core maths, worked examples at each concentration, and answers the questions people ask most about EOD microdosing.

Key takeaways

EOD = ~3.5 injections/week, so each shot is 100 ÷ 3.5 = 28.57 mg.
At 200 mg/mL: 0.143 mL → 14.3 units (draw to 14–15 u).
At 100 mg/mL: 0.286 mL → 28.6 units (draw to 28–29 u).
The weekly milligram total never changes — only how it is spread out.

Plug in your exact total and concentration with the Testosterone (TRT) microdosing calculator to get the unit fill for your own numbers.

The core math: 100mg/week split every other day

To run a Testosterone (TRT) microdose every other day from a 100 mg weekly total, you keep the prescribed weekly milligrams fixed and split them across more frequent, smaller injections. "Every other day" (EOD) means dosing on a roughly 2-day interval, which works out to about 3.5 injections per week.

The split is one division:

Weekly total ÷ injections per week = dose per injection
100 mg ÷ 3.5 = 28.57 mg per EOD injection (rounds to ~28–29 mg)

Splitting the same weekly milligrams into smaller, more frequent doses does not change the amount delivered over a week — only how it is spread out. Appraisals of depot testosterone esters note that infrequent injections produce supraphysiological peaks soon after the shot and subnormal troughs before the next — the rationale clinicians cite for more frequent dosing.³ For why a weekly figure is the anchor, see what mg per week means and what a split dose is. For much lower sub-therapeutic protocols, the women's low-dose testosterone microdosing calculator handles tiny draws down to 0.5 mg/week.

Why EOD is ~3.5 injections, not 4

A week is 7 days, so dosing every 2 days gives 7 ÷ 2 = 3.5 doses per week. Across a 14-day fortnight you inject 7 times (days 1, 3, 5, 7, 9, 11, 13) — exactly 3.5 per week.

Schedule	Injections/week	Dose per injection (100mg total)
Once weekly	1	100 mg
Twice weekly (E3.5D)	2	50 mg
Every other day (EOD)	3.5	28.57 mg
Daily	7	14.29 mg

For how these frequencies compare in practice, see daily vs twice-weekly vs every 3.5 days and the broader Testosterone (TRT) protocols explained overview.

How this is calculated: milligrams to units

Your syringe is marked in units (a U-100 insulin syringe), not milligrams. Two conversions get you there:

mg → mL: dose (mg) ÷ concentration (mg/mL) = volume (mL)
mL → units: volume (mL) × 100 = units (on a U-100 syringe, 1 mL = 100 units, so 0.01 mL = 1 unit)

The concentration printed on your vial label matters most. The two common testosterone cypionate strengths, 200 mg/mL and 100 mg/mL — both on the same FDA label² — give very different unit fills for the same 28.57 mg dose. See U-100 syringe units explained and how to read an insulin syringe if the markings are unfamiliar.

Worked examples: 28.57mg EOD by concentration

Each block runs the 28.57 mg EOD microdose through the two-step conversion, plus neighbouring split frequencies for context. The arithmetic is verifiable by hand.

Example 1 — 28.57mg at 200mg/mL

14.3 units

Inputs: 100 mg/week, EOD (3.5 shots/week), testosterone at 200 mg/mL.
Dose: 100 ÷ 3.5 = 28.57 mg. mg→mL: 28.57 ÷ 200 = 0.1429 mL. mL→units: 0.1429 × 100 = 14.3 units. Draw to the 14- or 15-unit mark on a 0.3 mL barrel.

Example 2 — 28.57mg at 100mg/mL

28.6 units

Inputs: same 100 mg/week and EOD schedule, but 100 mg/mL oil.
Dose: 28.57 mg (unchanged). mg→mL: 28.57 ÷ 100 = 0.2857 mL. mL→units: 0.2857 × 100 = 28.6 units. That is double the volume of Example 1 because the oil is half as concentrated — the milligram dose is identical.

Example 3 — twice-weekly at 200mg/mL

25 units

100 ÷ 2 = 50 mg. 50 ÷ 200 = 0.25 mL → 25 units. Moving to EOD nearly halves each fill (25 u → 14.3 u) for the same 100 mg/week.

Example 4 — daily at 200mg/mL

7.1 units

100 ÷ 7 = 14.29 mg. 14.29 ÷ 200 = 0.0714 mL → 7.1 units. A 0.3 mL (30-unit) syringe keeps that small fill readable.

Example 5 — 250mg/mL vial at EOD

11.4 units

Some vials are 250 mg/mL. 28.57 ÷ 250 = 0.1143 mL → 11.4 units. Higher concentration shrinks the fill, so dead space matters more.

Example 6 — rounding error per shot

≈ 0.5 mg

At 200 mg/mL, 14.3 units rounds to 14 u (28.0 mg) or 15 u (30.0 mg). Rounding the same way each shot keeps the weekly total within ~1–2 mg of 100 mg.

Example 7 — weekly back-check

100.0 mg

3.5 × 28.57 mg = 99.995 ≈ 100 mg/week; over a fortnight, 7 × 28.57 = 200 mg. The EOD split preserves the prescribed weekly milligrams.

Conceptual diagram (not to scale): the same 100 mg/week delivered as one weekly shot swings from high peaks to low troughs, while EOD 28.57 mg microdoses keep serum testosterone in a tighter band — the pharmacokinetic rationale behind more frequent dosing.^3,4

On a U-100 insulin syringe the scale runs 0–100 units across 1 mL, so 100 units = 1 mL. The shaded band marks the ~14-unit (0.143 mL) EOD fill for 28.57 mg at 200 mg/mL. The unit marks measure volume, not drug amount — the same mark holds a different dose at a different vial strength.

Per-injection units at a glance

Holding the 100 mg/week total constant, here is the EOD (28.57 mg) microdose in units for the two common concentrations, with other split frequencies for comparison.

Schedule (100mg/week)	Dose/injection	Volume @ 200mg/mL	Units @ 200mg/mL	Volume @ 100mg/mL	Units @ 100mg/mL
Twice weekly	50 mg	0.25 mL	25 u	0.50 mL	50 u
EOD (~3.5×/wk)	28.57 mg	0.143 mL	14.3 u	0.286 mL	28.6 u
Daily	14.29 mg	0.071 mL	7.1 u	0.143 mL	14.3 u

EOD fills land near 14 units at 200 mg/mL and ~29 units at 100 mg/mL, both fitting a 0.3 mL barrel. For choosing barrel size, see 0.3mL vs 0.5mL vs 1mL syringes.

Rounding, dead space, and accuracy notes

28.57 mg does not land on a whole unit at either concentration, so some rounding is unavoidable:

Round to the nearest readable mark the same way every time — that keeps your weekly total close to 100 mg.
Dead space wastes drug. The hub and needle retain a small volume; with tiny EOD fills this matters more, so low-dead-space insulin syringes help.
Never reuse a needle or syringe — use a fresh sterile single-use syringe each injection, per CDC safe-injection guidance.⁵
SubQ or IM both work — subcutaneous testosterone at IM-matching doses gives comparable serum levels.⁴
Confirm with the calculator. Enter your exact weekly total, EOD frequency, and vial concentration into the Testosterone (TRT) microdosing calculator for your specific numbers.

So, how do you microdose TRT on 100mg/week EOD?

Divide your 100 mg weekly total by 3.5 (the average number of every-other-day shots per week) to get 28.57 mg per injection. Convert that to syringe units using your vial concentration: at 200 mg/mL you draw to about 14 units; at 100 mg/mL you draw to about 29 units. The weekly milligram total does not change — only how it is spread across more frequent, smaller shots. Enter your exact weekly dose and vial strength into the Testosterone (TRT) microdosing calculator for your precise unit fill.

FAQs

How do you microdose TRT on 100mg/week EOD?

Divide 100 mg by 3.5 (the number of every-other-day injections in a week) to get 28.57 mg per shot. At 200 mg/mL that is about 14 units on a U-100 syringe; at 100 mg/mL it is about 29 units.

How many mg is each injection if I split 100mg/week EOD?

Every-other-day dosing is about 3.5 injections per week, so 100 mg ÷ 3.5 = 28.57 mg per injection, which rounds to roughly 28-29 mg. The weekly total stays at 100 mg.

How many units is a 28.57mg EOD microdose?

It depends on concentration. At 200 mg/mL it is 0.143 mL, or about 14.3 units on a U-100 syringe (draw to 14-15 units). At 100 mg/mL it is 0.286 mL, or about 28.6 units (draw to 28-29 units).

Does microdosing change my total weekly testosterone dose?

No. Splitting 100 mg/week into smaller EOD injections delivers the same 100 mg over the week. Only the per-injection amount and the spacing change, not the weekly total.

Why is EOD 3.5 injections instead of 4?

Dosing every 2 days across a 7-day week averages 7 ÷ 2 = 3.5 doses. Over a 14-day fortnight you inject 7 times, which is exactly 3.5 per week.

What syringe size suits these small EOD fills?

A 0.3 mL (30-unit) U-100 insulin syringe. EOD fills land near 14 units at 200 mg/mL and near 29 units at 100 mg/mL, both of which read clearly on a 0.3 mL barrel.

Sources

Bhasin S, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018;103(5):1715-1744. pubmed.ncbi.nlm.nih.gov/29562364.
DailyMed. Testosterone Cypionate Injection, USP (FDA label; 100 mg/mL and 200 mg/mL strengths). U.S. National Library of Medicine. dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a34023dc-fc54-4f66-bab0-9596502c23a3.
Nieschlag E, et al. Testosterone depot injection in male hypogonadism: a critical appraisal (peak-trough fluctuation). Clin Interv Aging. 2007;2(4):577-590. pubmed.ncbi.nlm.nih.gov/18225458.
Wittert G, et al. Testosterone Therapy With Subcutaneous Injections: A Safe, Practical, and Reasonable Option. J Clin Endocrinol Metab. 2022;107(3):614-626. pubmed.ncbi.nlm.nih.gov/34698352.
CDC. Safe Injection Practices — Injection Safety. www.cdc.gov/injection-safety/about/index.html.

This guide is for general educational purposes only and does not constitute medical advice. Always follow your prescriber's specific instructions.