PSA doubling time calculator
If PSA rises from 2 to 4 ng/mL in 90 days, it has doubled once, so the doubling time is 90 days, just under 3 months. Enter two PSA values and the days between them to get this two-point estimate. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Psa1
- 2
- Psa2
- 4
- Days
- 90
- Ratio
- 2
- Doublings
- 1
- Doubling time days
- 90
- Doubling time months
- 2.9568788501
Prostate-specific antigen doubling time, abbreviated PSADT, is the calendar time it would take for a measured PSA concentration to double if the recent exponential trend continued unchanged. Urology trainees, oncology students, and curriculum authors use that single number as a compact summary of how quickly two serial PSA values are rising in teaching cases and homework drills. This calculator accepts an earlier PSA, a later PSA, both in nanograms per millilitre, and the positive number of days between the two blood draws, then returns the two-point doubling time in months.
What PSA doubling time means and how the two-point formula works
The two-point prostate-specific antigen doubling time treats the recent PSA trajectory as a simple exponential: concentration grows by a constant multiplicative factor per unit time. Taking the natural log of both sides turns that assumption into a straight line in log-PSA versus calendar time, and the slope of the two-point line is ln of psa2 over psa1 divided by the elapsed days. Doubling time is then ln of two divided by that slope, which rearranges to days times ln of two over ln of psa2 over psa1.
Because clinical conversation reports PSADT in months, this capability divides the day result by 365.25 divided by 12, the mean Gregorian month length that includes a leap-day average. When psa2 equals psa1 the logarithm in the denominator is zero and the doubling time would be infinite; when psa2 is smaller the logarithm is negative and the quantity would describe a half-life, not a doubling. Always frame the month figure as an educational two-point estimate, not as a multi-value Memorial Sloan Kettering fit and not as a diagnosis.
Where a PSA doubling time calculator earns its keep
Urology and oncology classrooms use a PSA doubling time calculator so learners can check the two-point formula on textbook serial values without mixing log bases or forgetting the days-to-months conversion. Research assistants assembling synthetic prostate-cancer teaching datasets need stable PSADT labels from known triples without calling a live clinical service. If you later need cell-culture generation time, bacteria growth projections, or creatinine clearance, those are different search intents with their own pages rather than extra modes on this PSADT form.
Always present results as educational estimates from the two-point logarithmic identity; clinical decisions require qualified professionals, complete serial PSA histories, and local protocols this tool does not collect.
What you can do with it
Classroom and homework checks
Let students submit two PSA values in ng/mL and the days between them, then verify the two-point PSADT in months against textbook log arithmetic.
Synthetic teaching datasets
Bulk-produce stable PSADT-in-months labels from known psa1, psa2, and days triples without network calls or model drift.
FAQ
How is PSA doubling time calculated from two measurements?
Send finite positive psa1, psa2, and days. PSADT in days is days × ln(2) / ln(psa2/psa1).
What happens if the second PSA is not greater than the first?
A falling or unchanged pair would not yield a finite positive doubling time, so it is not billed as success.
Which units does the calculator use?
PSA values are nanograms per millilitre (ng/mL). The interval is in days.
Does this fit more than two PSA points?
No. This is the closed two-point formula only. Multi-value least-squares PSADT fits are a different method and are out of scope for this landing.
Why does the result use 30.4375 days per month?
That is 365.25 divided by 12, the average calendar month including leap years. The calculator shows this figure so you can see exactly how days were turned into months, instead of guessing whether 30 or 30.44 was used.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/health/psa-doubling-time \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"psa1":2,"psa2":4,"days":90}'const res = await fetch("https://api.kit.forhosting.com/health/psa-doubling-time", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"psa1": 2,
"psa2": 4,
"days": 90
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/health/psa-doubling-time",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"psa1": 2,
"psa2": 4,
"days": 90
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/psa-doubling-time", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"psa1":2,"psa2":4,"days":90}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"psa1":2,"psa2":4,"days":90}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/psa-doubling-time", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"psa1": 2,
"psa2": 4,
"days": 90
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "health.psa_doubling_time",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
The later value must be strictly greater than the earlier one; a falling or flat pair is rejected as invalid_input rather than a negative or infinite result.
What PSA doubling time means and how the two-point formula works
The conversion constant is returned as days_per_month so every client can audit the unit change instead of guessing whether the tool used 30, 30.44, or 365.25/12. Both cases fail with invalid_input naming psa2 versus psa1, matching the product rule that the second PSA must be strictly greater than the first. The implementation is closed-form floating-point arithmetic: no regression over extra points, no network, no wall-clock timestamps, and no random seeds, so identical triples always produce identical JSON after stable rounding to twelve decimal places.
Input contract, response shape, and error behaviour
POST a JSON body with three required finite numbers. Field psa1 is the earlier prostate-specific antigen in nanograms per millilitre; aliases first_psa, psa_first, initial_psa, and psa_initial are accepted. Field psa2 is the later PSA in the same unit; aliases second_psa, psa_second, final_psa, and psa_final are accepted. Field days is the positive elapsed interval in days between the two draws; aliases interval_days, elapsed_days, days_between, and t are accepted. Each field may arrive as a JSON number or as a numeric string. Missing fields, empty strings, non-finite values, non-positive PSA, and non-positive days fail with invalid_input naming the field and are not billed. On success the body echoes the cleaned psa1, psa2, and days; ratio as psa2 divided by psa1; doublings as log2 of that ratio; doubling_time_days from the two-point formula; doubling_time_months as days times ln of two over ln of the ratio times 365.25/12; days_per_month equal to 365.25/12; unit_doubling_time set to months; and a formula string restating the identity. A classic check is psa1 equals two, psa2 equals four, days equals ninety: the ratio is exactly two, there is one doubling, doubling_time_days is ninety, and doubling_time_months is ninety divided by 30.4375. Pair the JSON with your own charting if you need a log-PSA sketch; this endpoint computes the two-point month figure only. Successful API calls use the published $0.002 base price per item.
Where a PSA doubling time calculator earns its keep
Exam generators and learning-management plugins need a deterministic oracle that rejects a falling second PSA as invalid_input instead of silently emitting a negative month count that a buggy grader might treat as success.
Integration use cases
Exam and LMS auto-grading
Mark prostate-antigen doubling items with a deterministic oracle that rejects a second PSA that is not greater than the first as invalid_input.
Technical questions
What does the PSA doubling time calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.