8 Minute FTP Test Calculator

The 8-minute protocol is the short way into FTP: two maximal efforts instead of one long time trial, with the estimate taken at 90% of their average rather than 95%. Enter the average power of each effort:

The protocol

1. Warm up 15 to 20 minutes, with a few short accelerations.
2. First 8-minute effort at maximal sustainable power. Record the average.
3. Recover about 10 minutes at easy spinning.
4. Second 8-minute effort, same instruction. Record the average.
5. FTP = 90% of the mean of the two averages.

Efforts of 240 W and 225 W: the mean is 232.5 W, and FTP = 232.5 × 0.90 = 209.3 W.

The 10-minute recovery is part of the test, not a courtesy. The second effort is meant to start with some fatigue already in the legs, and the 90% factor assumes it. Riders who stretch the recovery to twenty minutes produce a higher second effort and an inflated FTP.

Why the discount is bigger than the 20-minute test’s

Both protocols answer the same question — what could you hold for an hour? — from different distances away from it. Eight minutes is far enough from 60 that a well-trained rider produces substantially more power than their threshold, so the correction has to be larger. Twenty minutes sits closer, and 5% is enough. Neither factor is measured on you individually; both are averages borrowed from populations, which is why the same rider can get slightly different FTPs from the two tests on the same day.

Where this test sits in the evidence

The 90% of 8 minutes convention is documented in the literature alongside the more common 95% of 20 minutes, and a 2022 review of cycling power profiling treats them as the two accepted single-effort field estimates of FTP. The same review is unenthusiastic about both: a single maximal effort describes one point on the power-duration curve, and the authors would rather riders model the curve from several efforts than convert one test into a threshold number.

Read practically, that means the 8-minute test is a tracking tool. Repeated with an identical protocol every four to eight weeks, the trend in the number tells you something real. Compared against a friend’s FTP from a different protocol, it tells you almost nothing.

When to choose it over the 20-minute test

Pick the 8-minute version when 20 continuous minutes at the limit is impractical — a trainer session squeezed into a lunch break, or a route with no uninterrupted 20-minute stretch. Pick the 20-minute test when you have never tested before, because it forgives an imperfect opening pace.

Either way, the output feeds the same place: the FTP training zones calculator for your seven zones in watts, and the watts per kilogram calculator if you want a number that compares across riders.