Estimate your FTP
Turn a 20-minute test, an 8-minute test, a ramp or a long ride into an FTP figure — and fit a Critical Power curve across several efforts to see where your power settles.
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The reference figures below still apply — they are part of the page, not the script.
Your best efforts
Average power for the whole effort — not a peak. Up to 5.
→ 20-minute test: 95% of your average power. Also feeds the Critical Power model.
1 of 5
The average power of the last full minute you completed. Not your best-ever minute — a ramp’s final minute is a different thing, and treating one as the other overstates FTP by around half.
Add an effort above — your estimate appears here.
Recommended FTP
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Estimates span
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Anaerobic capacity W′
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Model fit
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Every protocol that matched
Your power-duration curve
Show the numbers
| Duration | Power | Protocol matched | FTP estimate | In Critical Power fit |
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How this is calculated
- 20-minute test
- FTP = 0.95 × your average power. Applies to efforts of 18–22 minutes. The most reliable protocol here.
- 8-minute test
- FTP = 0.90 × your average power, for efforts of 7–10 minutes.
- Ramp test (MAP)
- FTP = 0.75 × the average power of the last full minute you completed.
- Long effort and the power-duration curve
- FTP = power ÷ the sustainable fraction for that duration, read off the same fatigue curve the climb calculator uses. That curve crosses 1.00 at about 47 minutes, because FTP is 40–60 minute power.
Two or more maximal efforts are fitted to P(t) = CP + W′/t, linearised as work against time (W = CP·t + W′) and solved by least squares. CP is the FTP estimate; W′ is the finite store of work available above it.
Only efforts between 2 and 22 minutes are fitted. Shorter ones inflate CP and collapse W′ — adding a 30-second sprint to a 5-minute and a 20-minute effort moves CP up 9 W and W′ down by a third. Longer ones do the reverse: one 60-minute ride drops CP by 29 W and inflates W′ to a figure no human has. Everything you enter is still plotted; the chart says which points were used.
The 8-minute constant (0.90) and this site’s fatigue curve disagree by 4.4%, so a 419-second effort and a 420-second one differ by about 24 W. 0.90 is the recognised published figure and is kept so the number matches other calculators. The 20-minute constant agrees with the curve to 0.25%.
Every one of these is an estimate from a single day’s effort. Pacing, heat, sleep and how hard you were actually willing to go all move the answer more than the choice of protocol does.
More tools: Training Zones Speed & Power Climb Calculator
Frequently asked questions
What is FTP?
Functional Threshold Power is the power you can hold for roughly 40 to 60 minutes. It is the number most training plans are built around, because the intensity of everything else is expressed as a percentage of it. Nothing on this page measures FTP directly — every protocol takes a shorter, harder effort and scales it.
Which test should I do?
A 20-minute all-out effort, if you can pace one. It is the protocol with the least scaling applied (FTP is 95% of your average power), it is the one this site's fatigue curve is calibrated against, and every other calculator uses the same constant, so the answer is comparable. An 8-minute test is easier to pace but needs a bigger correction, and a ramp test is easiest of all and needs the biggest.
Why does my 8-minute estimate disagree with my 20-minute one?
Partly you — holding 8 minutes hard is a different skill from holding 20 — and partly the maths. The published 8-minute constant of 0.90 and this site's own power-duration curve disagree by 4.4%, so a 419-second effort and a 420-second one come out about 24 W apart. The 0.90 is kept because it is the recognised figure and riders cross-check it elsewhere. When two protocols disagree, the estimator says so and tells you which one to trust.
What is W′?
W′ ("W prime") is the fixed amount of work, in kilojoules, you can do above Critical Power before you have to slow down. Think of it as a battery: Critical Power is what the engine sustains, W′ is what is left in reserve for attacks and finishes. Most trained riders land somewhere between about 10 and 30 kJ.
Why will it not fit a Critical Power curve to my efforts?
It needs at least two maximal efforts between 2 and 22 minutes, and one of them has to be at least twice as long as the other. Two efforts of similar length produce a mathematically valid line and a physiologically absurd rider — two 20-minute efforts can return a Critical Power 55 W below the power you actually held. Efforts shorter than 2 minutes or longer than 22 are still plotted on the chart; they are just not fitted, because the two-parameter model misbehaves at both ends.
Is the last minute of a ramp test the same as my best minute?
No, and treating them as the same is the single biggest error this tool avoids. A ramp's final minute is the point at which you can no longer hold the increasing target — it is not a maximal one-minute effort. A rider whose peak minute is 500 W does not have a ramp MAP of 500 W, and multiplying the peak minute by 0.75 overstates FTP by well over 100 W. That is why the ramp figure has its own field here and is never confused with a timed effort.
Know your number. Now use it.
An FTP figure is a starting point, not a plan. Ian works with riders to turn one into a season — structured, measured, and built round the time you actually have.