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How do you test your FTP indoors?

Updated 2026-10-23 · Sessions and training

Short answer

The common method is a 20-minute all-out effort: warm up thoroughly, ride as hard as you can hold for 20 minutes, then take about 95% of your average power as your FTP. Calibrate first, use a strong fan, and repeat the same protocol each time so the numbers compare.

Before you test at all

A test is only useful if it is repeatable, so the preparation matters as much as the effort.

Twenty minutes flat out is not an hour flat out: you can push harder over a shorter effort because part of it comes from a reserve that does not refill. The multiplier subtracts that borrowed power. It assumes your anaerobic capacity is typical, which is why the number is a starting point and not a measurement.

Calibrate the trainer, after at least ten minutes of warm-up, not from cold. See how to calibrate.
Set up a strong fan. A hot test gives a low number and tells you about your room, not your fitness.
Be reasonably fresh. Testing at the end of a heavy week measures your fatigue.
Note the conditions — fan, room, time of day, what you had eaten — and repeat them next time.
Do not test in ERG mode. You want to find your own ceiling, not have a number held for you.

A workable 20-minute protocol

20 minutes easy spinning, building gently.
3 x 1 minute fast-legged at high cadence, easy resistance, one minute easy between, to open the legs up.
5 minutes easy.
5 minutes hard — genuinely hard, around the effort you could hold for five minutes. This clears the top end so it does not distort the main effort.
10 minutes easy. Properly easy.
20 minutes as hard as you can sustain. This is the test.
10 to 15 minutes easy to finish.

Take the average power for the 20 minutes and multiply by 0.95. That is your estimated FTP.

Pacing it, which is where most tests go wrong

The commonest mistake is starting too hard, blowing up at eight minutes and limping to the end with a number well below what you are capable of.

Start at a power you think is slightly too easy. You should finish the first five minutes thinking you could have gone harder.
Aim to be even or slightly rising. The last three minutes should be the hardest.
If you have no idea where to start, use a previous FTP, or ride the first five minutes on feel at "hard but controlled" and read the number you settled at.
If you blow up, stop and test another day. A ruined test is not worth salvaging and the number will mislead you for weeks.

Alternatives, and whether you need to test at all

Ramp tests increase power steadily until you cannot continue, and estimate FTP from where you stopped. They are shorter and less unpleasant, and many people find them more repeatable. They can read slightly differently from a 20-minute test, which is fine as long as you stick to one method.

You may not need a formal test. If you do structured sessions regularly, you can set your zones from what you can actually complete, and adjust when sessions start feeling too easy. Plenty of people train well for years without ever doing a formal test.

What matters is that your numbers roughly reflect your current ability. An FTP that is 20 watts optimistic will quietly wreck every session you build on it.

Retest every six to ten weeks if you are training consistently, or whenever sessions start feeling clearly too easy or impossible.

A word on how hard this is

A proper 20-minute test is genuinely unpleasant and leaves most people fairly wrecked. That is normal.

What is not normal, and is worth stopping for, is chest pain, unusual breathlessness, dizziness, or feeling faint. If you are new to this kind of maximal effort, have not exercised hard in a long time, or have any known heart or blood pressure condition, speak to a doctor before doing an all-out test. Nothing here is medical advice.

Common questions

Why multiply by 95%?

FTP is roughly the power you could hold for about an hour, and most people can hold a bit more than that for 20 minutes. The 5% reduction is a convention that gets most people close.

Should I test indoors or outdoors?

Test where you train. If your sessions are indoors, an indoor number is the useful one. See why indoor FTP is usually lower.

How often should I test?

Every six to ten weeks is plenty when training consistently. Testing too often costs you training time and the number moves slowly anyway.

Is a ramp test as good as a 20-minute test?

For most purposes yes, and many people find it more repeatable. Just do not mix methods and then compare the numbers.

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