20-Minute FTP Calculator
Use your best average power from a 20-minute all-out cycling test to estimate Functional Threshold Power (FTP). This calculator uses the standard formula: FTP = 95% of 20-minute average power.
Tip: Re-test every 6-8 weeks to keep your training zones current.
What is FTP and why cyclists care
FTP (Functional Threshold Power) is the highest power you can sustain for about one hour in a steady effort. In practical training, FTP is used as a benchmark to set workout intensity, track progress, and compare performance over time. If your FTP goes up, your aerobic engine and fatigue resistance are likely improving.
A true 60-minute maximal test is tough, so many riders use shorter field tests. The most common is the 20-minute test, then applying a correction factor to estimate hour power.
How the 20-minute FTP calculation works
Core formula
The standard estimate is:
FTP = 20-minute average power × 0.95
Example: If your 20-minute power is 280 W, estimated FTP is 266 W.
Why 95%?
Most riders can hold a little more power for 20 minutes than for 60 minutes. The 5% reduction aims to bridge that gap. It is not perfect for everyone, but it is close enough for training prescriptions and trend tracking.
How to perform a good 20-minute FTP test
- Be rested: Avoid hard training 24-48 hours before testing.
- Warm up thoroughly: 15-25 minutes with a few short efforts.
- Pick stable conditions: Same trainer, fan setup, and bike position if indoors.
- Pace evenly: Start controlled for the first 3-5 minutes, then build.
- Use average power: Record your final 20-minute average, then calculate.
Understanding training zones from FTP
Once FTP is estimated, you can define power zones for structured workouts. These zones help you target specific adaptations:
- Zone 1 (Recovery): Easy spinning and active recovery.
- Zone 2 (Endurance): Aerobic base and long-ride durability.
- Zone 3 (Tempo): Steady, moderate work for muscular endurance.
- Zone 4 (Threshold): Raise sustainable power near FTP.
- Zone 5 (VO2 max): Increase oxygen uptake and high-end aerobic power.
- Zone 6+: Anaerobic capacity and neuromuscular efforts.
What counts as a “good” FTP?
Raw watts matter, but watts per kilogram (W/kg) are often more useful, especially for climbing and comparing riders of different sizes. A heavier rider may produce more total watts, while a lighter rider may have better W/kg.
Use this calculator’s optional body-weight input to estimate your FTP W/kg and monitor fitness trends over time.
Common mistakes that lower test accuracy
- Starting too hard and fading badly in the final 8-10 minutes.
- Testing in unusually hot conditions without cooling.
- Using inconsistent equipment or calibration between tests.
- Comparing indoor and outdoor data without context.
- Testing while overly fatigued or under-fueled.
How often should you re-test FTP?
Most riders test every 6 to 8 weeks. If your plan includes progressive overload and good recovery, this frequency is enough to update zones without excessive disruption. You can also monitor key workout performance weekly and test only when numbers clearly improve.
Final takeaway
The 20-minute FTP method is simple, practical, and highly useful for cyclists, triathletes, and indoor riders. Use the calculator above to estimate FTP, set zones, and train with purpose. Keep conditions consistent, test regularly, and focus on long-term trends rather than one perfect number.