PSA Doubling Time Calculator (PSADT)
Calculate PSA doubling time (PSADT) — how fast PSA is doubling — from two serial measurements. A shorter doubling time indicates more aggressive disease behaviour and influences decisions about active surveillance, salvage therapy and systemic treatment.
ng/mL
ng/mL
months
Time for PSA to double at the current rate of rise
- 1
PSA ratio (PSA₂ ÷ PSA₁)
4 ÷ 2 = 2 - 2
Natural log of ratio
ln(2) = 0.6931 - 3
PSA Doubling Time
12 × ln(2) ÷ 0.6931 = 12Time in months for PSA to double at the observed exponential rate.
How does this calculator work?
PSADT (months) = Δt × ln(2) / ln(PSA₂ / PSA₁). A doubling time below 3 months signals very aggressive progression; above 12 months is considered more indolent. PSA velocity (ng/mL/year) is also shown. Use serial measurements for reliable estimates.
Formula
How this is calculated
PSA doubling time (PSADT) models PSA rise as exponential growth: PSA(t) = PSA₁ × 2^(t / PSADT). Rearranging gives PSADT = Δt × ln(2) / ln(PSA₂/PSA₁), where Δt is the time interval between measurements and PSA₂ > PSA₁. A PSADT below 3 months is considered very aggressive and is associated with a high risk of distant metastasis; 3–6 months is aggressive; 6–12 months moderate; above 12 months is generally considered more indolent, and above 36 months is sometimes treated as clinically insignificant in the context of active surveillance.
PSA velocity (PSAV) — the absolute rate of rise in ng/mL per year — is a complementary metric. A velocity above 0.75 ng/mL/year in the PSA grey zone (4–10 ng/mL) has historically raised concern, though current guidelines place more weight on PSADT in post-treatment monitoring.
PSADT calculated from just two measurements can be imprecise due to biological and assay variability. For clinical decisions, most guidelines recommend using at least three PSA measurements over at least six months. The model assumes continuous exponential growth, which is a simplification — PSA can rise non-monotonically due to infection, inflammation, or test variability. This calculator is for informational purposes only; consult a urologist or oncologist for interpretation.
Frequently asked questions
PSADT below 3 months is generally considered very aggressive and warrants urgent specialist evaluation. PSADT between 3 and 6 months is aggressive; 6 to 12 months is moderate. Many active-surveillance protocols allow continued monitoring if PSADT is above 12 months, though the exact threshold varies by guideline, PSA level and patient context.
PSADT is most commonly used to monitor biochemical recurrence (BCR) after prostatectomy or radiotherapy — a PSA rise above a threshold (e.g., 0.2 ng/mL after surgery) signals possible disease return. PSADT helps predict the time to metastasis and guides the timing of additional treatment. It is also used in active surveillance protocols to detect disease reclassification.
The formula is undefined when PSA is stable (division by zero in the logarithm) and is meaningless when PSA is falling. A single rising measurement could reflect benign causes (prostatitis, urinary tract infection, recent prostate examination). Most guidelines recommend basing PSADT on a minimum of three measurements over six or more months to reduce measurement noise and confirm a true rising trend.
Also known as
TG we-Calculate Editorial Team. (2026). PSA Doubling Time Calculator (PSADT) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/psa-doubling-time-calculator
TG we-Calculate Editorial Team. "PSA Doubling Time Calculator (PSADT)." TG we-Calculate. 2026. https://we-calculate.com/calculator/psa-doubling-time-calculator.
TG we-Calculate Editorial Team, "PSA Doubling Time Calculator (PSADT)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/psa-doubling-time-calculator
@misc{wecalculate_psa_doubling_time_calculator, title = {PSA Doubling Time Calculator (PSADT)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/psa-doubling-time-calculator}}, year = {2026}, note = {TG we-Calculate} }
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