Compare tests using the same protocol. Calculated FTP, estimated FTP and a laboratory threshold are different references, even when their numbers look similar.
Three calculations, three assumptions
The 95% factor converts average power from a maximal 20-minute effort into a working FTP estimate. It depends on the protocol and execution. The best 20-minute section of an easy ride does not become a maximal test simply because software selects it.
For a TrainerRoad-style ramp protocol, a simplified reference is roughly 75% of the best one-minute power during the test. Do not apply this factor to a one-minute sprint record: the progressive test context matters. A well-paced maximal effort of approximately 60 minutes provides another sustained-power reference.
| Method | Input | Estimate |
|---|---|---|
| 20-minute test | Maximal 20-minute average power | × 0.95 |
| Compatible ramp test | Best minute in the progressive protocol | Approximately × 0.75 |
| 60-minute effort | Steady maximal average power | Observed value |
Why 95% is not an individual law
Borszcz and colleagues studied 23 trained cyclists and found substantial individual differences between the 20- and 60-minute methods despite similar group averages. A result can be repeatable and useful without precisely describing one-hour sustainable power.
Keep conditions comparable: power meter, recommended calibration, environment, warm-up protocol and pacing. Switching methods can move the number without representing an equivalent change in fitness.
EndurTrack eFTP: an estimate from your activities
EndurTrack looks for recent efforts at several durations in activities with power data. The engine combines references including 8- and 20-minute efforts with a critical-power fit when sufficient data exists. It displays supporting evidence and a confidence level instead of treating every number as equally certain.
Without recent maximal efforts, the absence of a new record does not prove declining fitness. Incomplete imports, a different meter or weeks without sustained work also limit interpretation. Configured FTP remains separate from the estimate: interval classification never changes it automatically.
Choose a working reference
Use a recent value consistent with your equipment and usual protocol. Then observe your sessions: do easy efforts remain easy, and are sustained blocks repeatable? Unusual difficulty can reflect fatigue as well as an unsuitable FTP setting.
Watts per kilogram adds a comparison relative to body mass. It does not describe aerodynamics, repeated acceleration ability or technical skill. The calculator shows this ratio if you enter your weight; the field is optional and does not change any account settings.
Common questions
What FTP does 300 W for 20 minutes give?
Using the 0.95 factor gives an estimate of 285 W. At 72 kg, that is approximately 3.96 W/kg.
Does eFTP replace testing?
It can provide a useful reference when recent reliable efforts are available. It cannot guarantee that an effort was maximal or make different protocols interchangeable.
Sources and editorial approach
The example weeks are educational EndurTrack proposals, not protocols validated for every individual. The sources below explain the principles and their limitations.
Read the EndurTrack method →