Is 95 % of 20-minute power accurate?

For most riders it lands within a few percent of a true hour power. Riders with a large anaerobic capacity overestimate — their 20-minute effort leans on it — and would do better with a 40–60 minute test, or a lactate test, which does not depend on pacing at all.

How often should I retest FTP?

Every six to eight weeks in a build, or whenever sessions at threshold start to feel clearly easier or harder than the zones say. A new test moves every zone with it.

Is FTP the same as LT2?

Close, not the same. LT2 is a physiological point read from blood lactate; FTP is a performance estimate from a time trial. They usually sit within a few percent of each other, and when they differ the lactate test is the one that explains why.

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FTP & Power Zones Calculator

Functional Threshold Power, W/kg and Coggan 7-zone model

FTP & power zones

Coggan 7-zone model from your best 20-minute power.

Best 20-min power (W)

Body weight (kg)

How the FTP calculator works

Functional Threshold Power is the highest power you can sustain for about an hour. The common field estimate is 95 % of your best 20-minute average power, ridden after a proper warm-up and a short hard effort to take the edge off anaerobic capacity. Enter that 20-minute value and your weight and the calculator gives FTP, watts per kilogram and the seven Coggan power zones built from it.

The zones scale from FTP: active recovery below 55 %, endurance to 75 %, tempo to 90 %, threshold to 105 %, VO₂max to 120 %, anaerobic capacity to 150 % and neuromuscular power above that. W/kg places you on the usual scale from recreational to world class — a rough reference, since aero drag decides flat speed and only climbing follows W/kg closely.

FTP is a good working number and a blunt one: it says nothing about where your aerobic threshold sits or how lactate behaves below it. A lactate test measures both thresholds directly; FTP usually lands close to LT2 but not on it.

Questions

Is 95 % of 20-minute power accurate?: For most riders it lands within a few percent of a true hour power. Riders with a large anaerobic capacity overestimate — their 20-minute effort leans on it — and would do better with a 40–60 minute test, or a lactate test, which does not depend on pacing at all.
How often should I retest FTP?: Every six to eight weeks in a build, or whenever sessions at threshold start to feel clearly easier or harder than the zones say. A new test moves every zone with it.
Is FTP the same as LT2?: Close, not the same. LT2 is a physiological point read from blood lactate; FTP is a performance estimate from a time trial. They usually sit within a few percent of each other, and when they differ the lactate test is the one that explains why.

Lactate analysis

LT1, LT2, OBLA from blood lactate step tests

Progress tracking

Fitness trends across weeks and months

Training zones

Power, HR and pace zones for every sport

Coach tools

Several athletes, shared test reports

Ready to track your full training load?

LaChart combines lactate testing, training analytics, Strava and Garmin sync and coach collaboration in one place.