Critical Power vs FTP: What Is the Difference (and Why It Matters)?
FTP is the most common number in cycling, but critical power (CP) is often more accurate for pacing and training. They are related, but not the same. Understanding the difference helps you set better training zones and avoid pacing mistakes.
Quick summary
FTP is practical. CP is physiological. Use the right tool for the job.
What FTP measures
FTP is an estimate of the highest power you can sustain for about 40-60 minutes. It is usually calculated from a time trial test or a ramp test using an FTP calculator. It is practical and useful, but it is not a precise physiological threshold.
What critical power measures
Critical power comes from modeling the relationship between power and time to exhaustion. It represents the boundary between heavy and severe intensity domains, and it is linked to a finite work capacity above CP (called W prime or W’).
In practice, CP often gives a better estimate of what you can sustain for hard efforts between 2-20 minutes, and how much “anaerobic battery” you have above that.
Why the difference shows up on the road
FTP is often estimated with a single test, and the result depends heavily on the test type. A ramp test can give a higher FTP than a 20-minute test for some riders. CP uses multiple efforts and fits a curve, which can be more stable across different test formats.
That is why FTP and CP can diverge. When they do, your pacing and interval targets can feel off if you rely on FTP alone.
| Metric | Best use | Typical test |
|---|---|---|
| FTP | Training zones | Ramp or 20-minute test |
| CP | Pacing and modeling | Multiple max efforts |
| W’ | Anaerobic capacity | Derived from CP model |
What the research says
Studies comparing FTP and CP show that they are correlated but not interchangeable. FTP can overestimate or underestimate the maximal metabolic steady state depending on the test used and the athlete. Recent evidence suggests FTP should not be treated as a direct physiological threshold.
Practical implications for cyclists
- Use FTP for broad training zones and long steady efforts.
- Use CP if you want more precise pacing for short, hard efforts.
- If your FTP feels too high for threshold work, CP might be a better anchor.
A simple way to use both
- Calculate FTP from a 20-minute test or ramp test.
- Estimate CP using multiple maximal efforts (for example 3, 7, and 12 minutes).
- If FTP and CP are close, you can use either.
- If FTP is 10% or more higher than CP, use CP for interval targets.
A simple CP testing week
- Day 1: 3-minute all-out effort (after full warm-up)
- Day 3: 7-minute all-out effort
- Day 5: 12-minute all-out effort
Use full recovery days between tests. Then plug the three efforts into our Critical Power & W′ Calculator to fit a power-duration curve and see your results instantly.
How W’ changes your pacing
W’ is the finite work you can do above CP. If you burn it all early, you will fade hard. This is why even pacing slightly below CP can beat an aggressive start in time trials and long climbs.
Simple pacing tip for long climbs
If you pace a climb based on FTP and it feels unsustainable after 10-15 minutes, try backing off to CP. Most riders can hold CP longer and with less fade. Your overall time is often better because you avoid late-race blowups.
Common testing mistakes
- All-out efforts too short. CP models are sensitive to test duration; you need a spread of efforts.
- Fatigued testing. Do tests when you are fresh to avoid underestimating CP.
- One-and-done testing. Re-test every 6-8 weeks to update the curve.
Related tools and guides
- Critical Power & W′ Calculator to estimate CP and W′ from your maximal efforts
- FTP Calculator for quick zone checks
- Climb Time Calculator to apply CP pacing on climbs
- VO₂max Training Guide for high-intensity interval prescription
Bottom line
FTP is practical. CP is physiological. Both are useful, but they answer different questions. If you want more accurate pacing and interval prescription, CP is worth the effort.