FTP from 20-Minute Test Calculator
Functional threshold power (FTP) is the cornerstone number in power-based cycling training: it is the highest average power, in watts, that you can sustain for about an hour, and almost every training zone is set as a percentage of it. Because a genuine one-hour test is brutal and hard to pace, most riders instead complete a 20-minute all-out effort and convert the result. You can hold more power for 20 minutes than for a full hour, so the convention is to take your 20-minute average power and multiply it by 0.95, trimming 5 percent to approximate true hour power. This calculator does exactly that: enter the average power you recorded across a clean, evenly paced 20-minute test and it returns your estimated FTP. The result is only as good as the test, so warm up fully, pace the effort evenly, and use the same trainer or route and a calibrated power meter each time you retest. Riders typically retest every four to six weeks to keep their zones accurate as fitness changes. Every figure here is computed deterministically from the standard 0.95 multiplier shown below, with a worked example that reconciles exactly to the calculator so you can follow each step.
FTP is estimated as 0.95 x your 20-minute average power. A 20-minute average of 280 W gives an estimated FTP of 266 W. Training zones are then set as percentages of this number.
FTP estimation formula
FTP = 0.95 x P20
P20 = average power over the 20-minute test (watts)
0.95 = standard factor that converts 20-minute power to hour power
The 0.95 factor reduces your best 20-minute power by 5 percent because power that can be sustained for a full hour is lower than power sustained for 20 minutes. The result is an estimate of the power you could hold at threshold for about 60 minutes.
Worked example
A rider completes an evenly paced 20-minute test and records an average power of 280 watts.
- Take the 20-minute average power: 280 W.
- Apply the standard factor: 280 x 0.95.
- Estimated FTP = 266 W.
The estimated FTP is 266 watts. These are the calculator's default inputs, so the result above matches the widget exactly.
Common training zones as a percentage of FTP
Once FTP is known, zones are set as a percentage of it. At an FTP of 266 W:
| Zone | % of FTP | Watts at 266 FTP |
|---|---|---|
| Active recovery | Up to 55% | Up to 146 |
| Endurance | 56 to 75% | 149 to 200 |
| Tempo | 76 to 90% | 202 to 239 |
| Threshold | 91 to 105% | 242 to 279 |
| VO2 max | 106 to 120% | 282 to 319 |
Activity guidance for adults: US Centers for Disease Control and Prevention.
FTP calculator: frequently asked questions
What is functional threshold power (FTP)?
Functional threshold power is the highest average power, in watts, that a cyclist can sustain for roughly one hour. It is the single most widely used reference number in structured cycling training, because training zones for endurance, tempo, threshold and intervals are all set as a percentage of FTP. A higher FTP for a given body weight means a stronger, faster rider.
Why is the 20-minute number multiplied by 0.95?
A true one-hour test is exhausting and hard to pace, so most riders use a 20-minute all-out effort instead. Because you can hold more power for 20 minutes than for a full hour, the 20-minute average is reduced by 5 percent (multiplied by 0.95) to approximate the hour power. The 0.95 factor is the long-standing convention popularised by power-based training methods.
How should I perform the 20-minute test?
Warm up thoroughly, then ride as hard as you can sustain evenly for a full 20 minutes on a flat road or trainer, recording your average power for that block. Avoid starting too fast. Some protocols add a short opening hard effort before the 20 minutes to fatigue the anaerobic system; this calculator simply takes the average power you enter and applies the 0.95 multiplier.
How often should I retest my FTP?
Every four to six weeks is common during a structured block, because fitness changes and stale zones make training less effective. Retest when workouts start to feel easy, after a recovery week, and when you are fresh rather than fatigued. Consistent conditions (same trainer, similar temperature, calibrated power meter) make the comparison meaningful.
Is FTP a measure of health or fitness?
FTP is a performance measure specific to cycling, not a clinical health metric. Regular aerobic exercise such as cycling supports cardiovascular health, and the US Centers for Disease Control and Prevention recommends at least 150 minutes of moderate-intensity activity each week for adults. Always train within your own limits and seek medical advice before starting hard testing if you have any health concerns.
Official sources
- Physical activity guidance for adults: US Centers for Disease Control and Prevention (CDC). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.