PSA doubling time calculator, with PSA velocity
PSA doubling time is how long your PSA takes to double, and PSA velocity is how much it rises in a year. Neither is printed on a lab report. Both come from a series of results and their dates, so you can work them out yourself. Enter up to six PSA results below, each with the date it was drawn. Empty rows are ignored, and the order doesn’t matter. The example filled in is the one worked through further down.
The formula
The calculator follows the PSA Working Group, a 2006 National Cancer Institute conference that set out how doubling time should be calculated:
PSA doubling time (months) = ln(2) ÷ the slope of ln(PSA) against time in months
The slope is a least-squares line through all the points, the same fit a spreadsheet’s SLOPE function gives, not just the first and last result. ln is the natural log, and ln(2) is about 0.693. Velocity is the same kind of fit on the plain values:
PSA velocity (ng/mL per year) = the slope of PSA against time in years
PSA in µg/L is the same number as ng/mL, so either unit works. The calculator counts a month as 30.44 days, a twelfth of a year.
Doubling time and velocity measure different things
Velocity is a change in ng/mL. Doubling time is a change in percentage. A PSA that goes from 0.20 to 0.40 in eight months has a velocity of only about 0.30 ng/mL per year, but it doubled in eight months. A PSA that goes from 5.0 to 5.3 in a year has the same velocity, yet at that rate it would take about 143 months, or 12 years, to double.
Doubling time is the measure used after treatment, when PSA starts near zero and a small rise can be a fast one. Velocity was proposed for screening, where it did not hold up, as covered below.
The Working Group rules
The Working Group set minimums for a doubling time to mean anything. The calculator checks each one and says which a series misses:
- At least three PSA values, at least 4 weeks apart, spanning at least 3 months.
- Every value 0.20 ng/mL or higher. Near zero, a small error in the test is a large percentage of the result.
- All values from up to the past 12 months, not just the ones that rose. A series that wobbles still counts. The 12-month limit is there because doubling time can change, and the recent period reflects current disease activity. The calculator still gives a result for a longer span, but warns you.
- The same assay, preferably the same lab. The calculator can’t check this one.
Treatments that move PSA, such as finasteride or testosterone, should be steady over the period. Two results from the same day are averaged.
A worked example
Suppose PSA after surgery reads 0.20, then 0.28 four months later, then 0.40 four months after that. These are the values the calculator starts with.
| Date | Months | PSA (ng/mL) | ln(PSA) |
|---|---|---|---|
| Jan 15, 2026 | 0 | 0.20 | −1.609 |
| May 15, 2026 | 3.94 | 0.28 | −1.273 |
| Sep 15, 2026 | 7.98 | 0.40 | −0.916 |
The slope of ln(PSA) against months is about 0.0868 per month. Doubling time is 0.693 ÷ 0.0868, or about 8.0 months, which matches the eye: PSA went from 0.20 to 0.40 in eight months. The slope of PSA against time gives a velocity of 0.30 ng/mL per year.
When PSA is falling or flat
If the line through ln(PSA) is flat or slopes down, there is no doubling time. The Working Group notes that a zero or negative slope makes the estimate nonexistent or negative, so the calculator reports that PSA is not rising instead of printing a negative number. For a falling PSA it also gives the halving time, the months PSA takes to fall by half at the same rate. Reverse the example above, 0.40 down to 0.20, and it halves in about 8.0 months.
Where doubling time matters
Doubling time is used mostly after surgery or radiation, once PSA has started to come back, which is called biochemical recurrence. In a study of 379 men whose PSA returned after surgery, Freedland and colleagues found that doubling time, the Gleason score, and how soon after surgery PSA came back all predicted death from prostate cancer. A doubling time under 3 months carried the highest risk, and one of 15 months or more the lowest. The authors also noted that survival in the lowest-risk men can be very long. Your care team uses doubling time with the rest of your history to judge how soon a returning PSA needs attention.
After radiation, the prostate is still there and PSA rarely falls to zero. The Working Group mentions subtracting the lowest value after treatment from each result before calculating, as one way to compare with men treated by surgery. This calculator doesn’t do that, so ask your care team which approach they use.
Why velocity is not a screening trigger
Velocity was once a reason for biopsy on its own, even with a normal PSA. In a study of 5,519 men from the Prostate Cancer Prevention Trial who all had biopsies, Vickers and colleagues found that adding velocity barely improved the prediction of cancer, and that biopsying men for a high velocity alone would mean biopsying close to one man in seven. They concluded it should not be in practice guidelines. The AUA/SUO early detection guideline now recommends against using velocity as the only reason for further testing or biopsy during screening. A rising line is a reason to talk with your clinician, and to repeat the test, not a verdict.
When the numbers mislead
- A change of lab or assay. PSA tests are calibrated to different standards. In a 2008 study, the same blood measured about 20 percent lower with a test calibrated to the WHO standard than with the older Hybritech calibration. A switch partway through a series can make PSA look like it fell or rose when nothing changed, and the doubling time with it. Calculate from one assay, and start a new series at a switch.
- One high result. Infection, a catheter, or a biopsy can raise PSA for a while, and a single spike pulls the line up. Repeat a surprising result first.
Tracking PSA over time
How to track your PSA over time covers what counts as a real change, what else moves PSA, and what to record with each result.
PSA in HealthViewer
HealthViewer is a lab results tracker that runs on your own computer. It imports PSA results from lab report PDFs, MyChart downloads, and direct connections to your health system, and charts them by date in Trends, with journal notes to mark a change of lab.
Everything stays in an encrypted file on your computer, with no account and no cloud service. Getting Started walks through the first import.
This calculator is for understanding your results, not for diagnosis or treatment. Talk to your clinician about what your PSA doubling time or velocity means for you.