FTP calculator

How this is calculated

FTP is taken as 95% of your best 20-minute average power. That is the whole formula, and it is worth understanding rather than trusting.

The 5% haircut exists because twenty minutes is not an hour. Most riders can hold noticeably more power for twenty minutes than they could sustain for sixty, so the raw twenty-minute figure would place every training zone slightly too high. The correction is a convention that the sport settled on — not a measurement, and not derived from your physiology in particular.

Watts per kilogram is simply your FTP divided by your body weight. It is the more useful number the moment the road points up, and the less useful one on the flat.

How to ride the test so the number means something

The arithmetic is trivial. Producing an honest twenty minutes is not.

• Warm up properly. Fifteen to twenty minutes with a few short openers. Going in cold costs you watts you actually have.
• Pace it evenly. The most common mistake is starting on the number you hope for. If the last five minutes are a collapse, the average is not a threshold — it is a story about your first five minutes.
• Repeat the conditions. Same trainer or same climb, similar temperature, similar time of day, similar state of rest. A trend measured consistently is worth more than one accurate number you cannot compare to anything.
• Do not test tired. A test at the end of a heavy block measures your fatigue, and then every zone inherits it.

How accurate is this, honestly

Worth knowing before you treat the output as a measurement.

A laboratory study compared FTP — taken exactly as this calculator takes it, 95% of a 20-minute time trial — against critical power in 17 moderately trained cyclists and triathletes. On average they agreed well: a mean difference of 7 ± 13 W and a very strong correlation (r = 0.969). But the limits of agreement ran from −19 to +33 W, and the typical error was 13 W, or 5.6% — which the authors point out sits above the 5% usually accepted in sport science. Their own wording is careful but pointed: arguably, they write, these findings question the underlying physiology of the FTP concept (Front Physiol, 2020).

🔴 The limits: 17 riders, one laboratory, moderately trained, a single study. It does not make FTP useless — an anchor only has to be stable enough to train from. It does mean the number this page gives you is a working reference you adjust by feel and results, not something measured. That is also why the output is rounded to whole watts.

Where you test changes the answer

If your outdoor numbers beat your indoor ones, that is not necessarily your trainer reading low.

Nine junior road cyclists completed a full laboratory series and then a 20-minute time trial on an uphill road. Outdoor FTP came out at 269 ± 34 W against a laboratory critical power of 236 ± 24 W and a 4-mmol lactate power of 233 ± 23 W — 14–15% higher — and the outdoor 20-minute power was 12% above what the indoor power–duration relationship predicted (J Strength Cond Res, 2023).

🔴 Nine male juniors on one climb: the direction is worth carrying, the percentage is not. The practical rule holds either way — test in one environment and compare like with like. If you set your zones from an outdoor test, expect indoor sessions at those targets to feel harder than they should.

What to do with the number

On its own an FTP figure does nothing. It is an anchor: every training zone is defined as a percentage of it, which is also why an inaccurate FTP misplaces all of them at once.

The next step is turning it into watt ranges you can actually ride to — that is the cycling training zones calculator. If you want the background rather than the numbers, cycling training zones explained covers what each band is for, and what is FTP in cycling covers the test itself in more depth.