Calculator

TRT Protocol Optimizer

See where your testosterone sits across the dosing cycle. Anchor the curve to your own labs or model a protocol change before committing.

e.g., 100 mg. This is the amount per single injection, not total weekly dose.

SubQ produces a flatter curve with ~15-20% lower peak and ~10-15% higher trough compared to IM at the same dose.

Used for age-adjusted reference bands

Optional: anchor to your labs

Drawn the morning of your injection, before injecting

Optional. Drawn 24-48 hours after injection

With just a trough, the calculator estimates your peak from population data. With both a peak and trough, it back-calculates your personal half-life for a more accurate curve.

Compare frequencies (same weekly dose):
Estradiol management: More frequent injection schedules (daily, EOD, twice-weekly) produce flatter testosterone curves, which reduces aromatization peaks and may lower estradiol-related side effects (water retention, gynecomastia, mood changes). If estradiol management is a concern on your current protocol, increasing frequency before adding an aromatase inhibitor is the preferred first step.
Lab timing guidance: For trough measurement: draw blood the morning of your injection, before injecting. For peak: draw 24 to 48 hours after injection. For daily SubQ protocols, any morning draw reflects steady-state. For undecanoate (Aveed), draw just before the next scheduled injection.
About the reference ranges: This calculator shows two reference ranges. The lab reference low (264 ng/dL) is the floor used by most commercial labs, based on current population data. The green age-adjusted band shows where a healthy male your age would likely sit based on 1980s cohort data (Massachusetts Male Aging Study), before the well-documented secular decline of approximately 1% per year in population testosterone levels. This decline is partly attributed to rising rates of obesity and insulin resistance, and partly to environmental endocrine disruptors (phthalates, BPA, microplastics). Neither range is a treatment target; both are context for the conversation between you and your prescriber.

Topical testosterone requires daily application to maintain stable levels.

Optional: anchor to your labs

Drawn 2-8 hours after your morning application

Skin-to-skin transfer risk (FDA black box warning): Testosterone gel and cream can transfer to others through direct skin contact, particularly to women and children. This can cause virilization in children (early puberty, genital enlargement, aggressive behavior) and virilization in female partners. After application: wash hands thoroughly with soap and water, cover the application site with clothing, wait at least 2 hours before skin-to-skin contact, and wash the area before contact if possible.
Lab timing: Draw labs 2 to 8 hours after your morning application (Endocrine Society 2018). This captures the post-application peak and gives the most clinically useful snapshot of your steady-state level.
Topical testosterone produces flatter, more stable levels than injections but has lower bioavailability (~9-14% for gel) and requires daily application. Individual absorption varies widely; some patients absorb well on gel while others need to switch formulations or routes.
Off-label use: No testosterone product is currently FDA-approved for use in women. Testosterone therapy in women is prescribed off-label based on clinical evidence. This calculator uses dosing ranges from the 2019 Global Consensus Position Statement on testosterone therapy for women (Davis et al.).

Typical: 5 (0.5%), 10 (1%), or 20 (2%)

Typical: 0.25 to 0.5 g

Optional: current lab values

Lab timing: Draw labs at trough, before the next application, in the morning.
Evidence supports testosterone therapy for hypoactive sexual desire disorder (HSDD) in postmenopausal women (Davis 2019, Global Consensus). Insufficient evidence currently exists for other indications including mood, energy, or bone density (Endocrine Society 2019). Oral testosterone and methyltestosterone are not recommended for women due to hepatic first-pass effects and adverse lipid impact.

Standard range: 6 to 12 pellets. Each pellet contains 75 mg testosterone (Testopel).

10
Total dose: 750 mg

Level at which you'd consider re-pelleting. Default 400 ng/dL.

Optional

For calendar-based re-pellet timing

How long your last pellets lasted before symptoms returned

Lab timing: Check levels at 4 to 6 weeks post-implant (near peak) and again at the first sign of symptom return. The trough lab helps calibrate your personal duration for the next cycle.
Pellets provide the most stable testosterone levels of any delivery method but require an in-office procedure every 3 to 6 months. Common side effects include pellet extrusion (5-12% of insertions) and site infection (less than 1%).

How this works

Injectable testosterone

Injectable testosterone esters are oil-based depot formulations. After injection, the ester chain is cleaved by tissue esterases, gradually releasing free testosterone into circulation. Longer ester chains produce slower release: undecanoate (longest) has a half-life around 34 days, while propionate (shortest) clears in roughly 2 days. Cypionate and enanthate sit in the middle at 7 to 8 days and account for the vast majority of TRT prescriptions.

The pharmacokinetic curve shows your serum testosterone from one injection to the next. After a cypionate or enanthate injection, testosterone rises over the first 24 to 48 hours as the ester depot releases drug, then falls exponentially as your body metabolizes and eliminates it. The lowest point, the trough, occurs just before your next injection. This is the most common lab draw timing.

Injection frequency determines the shape of this curve. A single 200mg weekly injection produces a tall peak and a deep trough, with serum testosterone potentially spanning 500 ng/dL or more across the week. Splitting the same 200mg into two 100mg doses (every 3.5 days) delivers the same total weekly testosterone but with a much flatter curve: lower peaks, higher troughs, and less overall fluctuation. The extreme version is daily subcutaneous microdosing, which approximates a steady state. This matters because symptom control often correlates with trough level and with minimizing large swings.

Subcutaneous injection produces a flatter curve than intramuscular. The subcutaneous fat depot releases testosterone more slowly than muscle tissue, resulting in a lower peak and a higher trough at the same dose. Many clinicians now prefer SubQ for patients on frequent protocols.

When you enter your own lab values, the calculator anchors the curve to your data instead of population estimates. With a trough value alone, it estimates your peak using the population half-life. With both a peak and a trough, it back-calculates your personal elimination rate. Your personal half-life may differ from the population average depending on body composition, sex hormone-binding globulin (SHBG) levels, hepatic metabolism, and injection technique (depth, location, massage).

For testosterone undecanoate (Aveed), the loading protocol models the FDA-approved initiation sequence: an initial dose, a second dose at week 6, then maintenance doses every 10 to 14 weeks. Because of the long half-life (~34 days), levels accumulate across the loading phase before reaching steady state.

Topical testosterone

Gels and creams deliver testosterone through the skin, maintaining relatively stable serum levels with daily application. Bioavailability is low (typically 9 to 14% for commercial gels), meaning most of the applied testosterone does not reach systemic circulation. Individual absorption varies widely based on skin thickness, body hair, sweating, and application technique. The calculator uses FDA prescribing information data for commercial products and dose-proportional estimates for compounded preparations. Scrotal skin absorbs approximately 5 to 8 times more testosterone than non-genital skin due to its thinner stratum corneum, which is why compounded scrotal cream can achieve therapeutic levels at lower applied doses.

Testosterone for women

Women produce testosterone at roughly one-tenth the level of men, primarily from the ovaries and adrenal glands. Testosterone declines with age, particularly after menopause. The women's tab uses the 2019 Global Consensus target of restoring levels to the premenopausal physiological range (15 to 70 ng/dL) rather than using male reference ranges. Doses used in women (typically 0.5 to 5 mg/day applied) are much lower than in men, and monitoring focuses on avoiding supraphysiological levels that increase the risk of androgenic side effects.

Pellet testosterone

Subcutaneous testosterone pellets (Testopel, 75 mg each) are implanted in the hip or gluteal fat pad and dissolve slowly over months. The PK model uses a two-phase approach: a near-linear rise over the first 4 to 5 weeks as pellets establish surface dissolution and vascularize, followed by an exponential decay phase as pellet mass decreases. Duration depends on pellet count, body composition, and individual metabolism. The calculator projects serum levels with a confidence band (plus or minus 20%) reflecting interindividual variation, and estimates when levels will cross below your target trough to help time re-pelleting.

Age-adjusted reference bands

The age-adjusted reference bands in this calculator are derived from the Massachusetts Male Aging Study (MMAS), one of the largest longitudinal testosterone studies ever conducted, published by Travison et al. in 2007. This study documented a population-level decline in testosterone of approximately 1% per year, independent of aging, starting in the 1980s. Possible contributing factors include rising obesity and insulin resistance rates and increasing environmental exposure to endocrine disruptors such as phthalates, BPA, and microplastics. Because modern lab reference ranges are derived from today's lower-testosterone population, a man in his 40s with a level of 350 ng/dL might fall within the lab's "normal" range but below what a healthy man his age would have measured in 1988.

References

Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715-1744.

Travison TG, Araujo AB, O'Donnell AB, et al. A population-level decline in serum testosterone levels in American men. J Clin Endocrinol Metab. 2007;92(1):196-202.

Shoskes JJ, Wilson MK, Spinner ML. Pharmacology of testosterone replacement therapy preparations. Transl Androl Urol. 2016;5(6):834-843.

Davis SR, Baber R, Panay N, et al. Global consensus position statement on the use of testosterone therapy for women. J Clin Endocrinol Metab. 2019;104(10):4660-4666.

Wierman ME, Arlt W, Basson R, et al. Androgen therapy in women: a reappraisal. An Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2014;99(10):3489-3510.

Testosterone undecanoate injection (Aveed). FDA prescribing information. Endo Pharmaceuticals, revised 2023.

Testosterone topical gel 1% (AndroGel). FDA prescribing information. AbbVie Inc., revised 2023.

Testosterone topical gel 1.62% (AndroGel). FDA prescribing information. AbbVie Inc., revised 2023.

Kuhnert B, Byrne M, Simoni M, et al. Testosterone substitution with a new transdermal, hydroalcoholic gel applied to scrotal or non-scrotal skin. Eur J Endocrinol. 2005;153(2):317-326.

McCullough AR, Khera M, Goldstein I, et al. A multi-institutional observational study of testosterone levels after testosterone pellet (Testopel) insertion. J Sex Med. 2012;9(2):594-601.

Handelsman DJ, Conway AJ, Boylan LM. Pharmacokinetics and pharmacodynamics of testosterone pellets in man. J Clin Endocrinol Metab. 1990;71(1):216-222.