DHT Reduction Calculator
Clinically grounded: Values are based on published phase-III trial averages (Kaufman 1998, Gormley 1992). Individual variation exists. Reviewed by our medical team. Not a substitute for medical advice.
Finasteride blocks 5-alpha reductase type II, the enzyme that converts testosterone to dihydrotestosterone (DHT). The tool below estimates your expected DHT reduction based on dose and compartment.
Estimate DHT Reduction
1 mg/day (Propecia — FDA-approved for AGA) 5 mg/day (Proscar — FDA-approved for BPH)Typical male serum DHT: 250–900 pg/mL (25–90 ng/dL). Leave at 300 pg/mL if unknown.
Understanding the numbers
| Dose | Serum DHT ↓ | Scalp DHT ↓ | Prostate DHT ↓ | PSA ↓ |
|---|---|---|---|---|
| 1 mg/day | ~70% | ~64% | — | ~41% |
| 5 mg/day | ~73% | ~73% | ~80% | ~50% |
The difference between 1 mg and 5 mg in serum DHT suppression is modest (~70% vs ~73%). This is because 5-alpha reductase type II is nearly saturated at 1 mg. Where the doses diverge is prostate tissue DHT, where 5 mg achieves ~80% reduction — which is why the higher dose is used for BPH.
PSA and finasteride — what you must know
Critical PSA note: Finasteride reduces serum PSA by approximately 41% (1 mg) or 50% (5 mg) after 6 months of use. Any clinician interpreting PSA in a patient taking finasteride must apply the correction factor. Failure to do so can mask clinically significant PSA elevations. Do not stop finasteride prior to a PSA test — the correction formula is more reliable than stopping the drug.
Frequently asked questions
How accurate is this calculator?
The estimates use published population averages from phase-III trials. Individual DHT suppression varies based on genetics, body composition, and CYP3A4/UGT enzyme activity. The calculator is a reference tool — not a diagnostic test.
Why is scalp DHT reduction different from serum?
The scalp’s sebaceous glands and hair follicles contain their own 5-alpha reductase activity. Studies using scalp biopsy show that even though 1 mg finasteride reduces serum DHT by ~70%, scalp DHT is reduced by ~64% — slightly less efficient penetration of the enzyme compartment. Topical finasteride formulations target this compartment more directly.
Does a higher DHT reduction mean better hair results?
Not necessarily. The 1 mg vs 5 mg difference in scalp DHT is modest (~64% vs ~73%), and head-to-head hair loss trials have not shown meaningful superiority of 5 mg for AGA. The extra DHT suppression at 5 mg mainly benefits prostate tissue. For AGA, 1 mg is the standard evidence-based dose.
How long does it take to reach full DHT suppression?
Steady-state finasteride plasma levels are reached within 7–8 days. DHT suppression follows the same timeline. By day 7, serum DHT is already reduced by approximately 65–70% on 1 mg. Maximum suppression is maintained indefinitely with continued use and reverses within 2 weeks of stopping.
Sources: Kaufman KD et al. J Am Acad Dermatol. 1998;39(4):578–589. Gormley GJ et al. N Engl J Med. 1992;327(17):1185–1191. Rittmaster RS et al. J Clin Endocrinol Metab. 1991;72(3):503–509. Clark RV et al. J Clin Endocrinol Metab. 2004;89(5):2179–2184.
Related: How finasteride works | Dosage guide | Finasteride 1 mg | Finasteride 5 mg | Topical finasteride