FTP calculator

Put in what you held and which test you did. You get your threshold power, your watts per kilogram and all six training zones.

## What FTP actually means

Functional Threshold Power is the highest average power you could hold for about an hour without blowing up. That is the whole definition. Everything else — the tests, the multipliers, the apps — exists because almost nobody is willing to ride flat out for an hour to find out.

It matters because it is the number every structured session is written against. "Four by eight minutes at 105 per cent" means nothing until you know what 100 per cent is. Get FTP wrong by twenty watts and every session you do afterwards is either too easy to work or too hard to finish.

## Why the tests have multipliers

Twenty minutes flat out is not the same as an hour flat out. You can push harder over a shorter effort because you are partly spending a reserve that does not refill — the anaerobic contribution. The multiplier is there to subtract that borrowed power and leave the part you could have sustained.

• 20 minutes × 95% is the standard, from Allen and Coggan's work. Ride twenty minutes as hard as you can hold evenly, take the average, remove five per cent.
• Ramp test × 75% of your best minute has become the common one because it takes about fifteen minutes and needs no pacing judgement at all. You simply ride until you cannot.
• 2 × 8 minutes × 90% uses the second effort, because the first one tells you more about your optimism than your threshold.
• 30 minutes × 93% sits between the twenty and the hour.
• A full hour needs no multiplier, because it is the definition.

## The multipliers are averages, and you are not an average

This is the part most calculators leave out, and it matters more than the arithmetic.

The 95 per cent figure assumes your anaerobic capacity is typical. If you are a sprinter — big, punchy, good at short efforts — you will pull a twenty-minute number well above your real threshold, and 95 per cent of it will still be too high. If you are a diesel, happiest grinding away for hours with no top end at all, the opposite happens and the test undersells you.

So treat the output as a starting point to adjust, not a measurement. The test that matters is the next three weeks of sessions. If the four-by-eights at threshold feel comfortably repeatable, your FTP is higher than this says. If you are falling apart in the third interval every time, it is lower. Move it by five or ten watts and try again.

## How to ride the test so the number means something

Most bad FTP numbers come from bad pacing, not bad maths.

Go out too hard and you will fade, and the average will be lower than what you could have held evenly — you will have ridden a twenty-minute test as two very different ten-minute efforts. The fix is dull and reliable: pick a number you think you can hold, hold exactly that for the first five minutes even though it feels easy, and only lift it in the last three.

Warm up properly. Twenty minutes of easy riding with two or three short hard efforts in it. A cold test is a low test.

Use the same conditions every time. Same trainer, same fan, same bike, same time of day, same approximate state of your legs. FTP is only useful as a comparison with your own previous FTP, and a number taken in a hot room after a hard weekend is not comparable to one taken fresh.

Expect indoors to be lower. Most riders test five to ten per cent below their outdoor figure, and that is normal rather than a failure. Heat is the main culprit.

## How often to retest

Every six to eight weeks is plenty while you are training consistently. More often than that and you are mostly measuring how tired you are. Less often and your zones drift out of date.

If a block has gone well you will usually feel it before you test it: the same session at the same watts stops hurting in the same way. That feeling is the cue to retest, not the calendar.