Calculate PSA velocity from two prostate-specific antigen results and the time between tests, or solve for the later PSA or interval, in ng/mL per year.
Medical note: This calculator reports an annualized two-result arithmetic change, not a diagnosis. Clinical trend assessment may use additional measurements. For prostate-cancer screening, PSA velocity should not be the sole indication for a secondary biomarker, imaging, or biopsy; discuss the full PSA series and testing context with a licensed clinician.
PSA Velocity Formula
PSA velocity is the average rate of change in prostate-specific antigen (PSA) between two test results. In plain terms, it tells you how quickly the later PSA value is rising or falling relative to the earlier value over a measured time interval.
| Variable | Description | Common Unit |
|---|---|---|
| PSAV | PSA velocity, or the average change in PSA per unit of time | ng/mL/year, ng/mL/month, or ng/mL/day |
| PSA1 | Earlier PSA measurement | ng/mL |
| PSA2 | Later PSA measurement | ng/mL |
| t | Elapsed time between the two tests | years, months, or days |
The calculator converts an entered interval in months or days to years and reports an annualized two-result change in ng/mL/year.
How to Calculate PSA Velocity
- Enter the earlier PSA result as PSA1.
- Enter the later PSA result as PSA2.
- Enter the exact time between the two tests in years, months, or days.
- Subtract the earlier PSA from the later PSA.
- Divide that difference by the elapsed time.
This means the calculator is finding the slope between two points: the change in PSA over the change in time.
Interpreting the Result
- Positive PSA velocity: the later PSA is higher than the earlier PSA.
- Zero PSA velocity: there is no net change between the two results.
- Negative PSA velocity: the later PSA is lower than the earlier PSA.
Example Calculation
Assume an earlier PSA result of 4.2 ng/mL, a later PSA result of 5.1 ng/mL, and an elapsed time of 18 months.
If you prefer the monthly rate for the same data:
Why the Time Interval Matters
The same PSA change can produce very different velocity values depending on how much time passed between tests. A shorter interval creates a larger rate, while a longer interval creates a smaller rate.
| Scenario | Result |
|---|---|
| PSA increases by 1.0 ng/mL over 1 year | PSAV = (1.0) / (1) = 1.0 ng / mL / year |
| PSA increases by 1.0 ng/mL over 2 years | PSAV = (1.0) / (2) = 0.5 ng / mL / year |
Practical Tips for Using the Calculator
- Use the earlier lab result for PSA1 and the later lab result for PSA2.
- Make sure both PSA values are in the same unit, typically ng/mL.
- Use the actual time elapsed between the tests instead of rounding too aggressively.
- If your tests are several months apart, entering months directly can reduce conversion mistakes.
- A two-point velocity is an average change over one interval, not a complete long-term trend.
What This Calculator Tells You
- The net PSA change between two dates
- The average rate of that change
- Whether the change is upward, flat, or downward
- The annualized two-result rate in ng/mL/year
Important Context
This calculator is useful for quantifying change, but it does not identify the reason for that change. It is best viewed as a math tool for trend estimation between two measurements. Because PSA interpretation depends on clinical context, testing conditions, and the broader pattern over time, this result should be discussed with a licensed clinician rather than used alone to make medical decisions.
