Cycling Power Duration Curve Calculator
Estimate the maximum sustainable power you can hold for any duration from a 1-minute sprint to a multi-hour ride, using your FTP and anaerobic capacity. Ideal for race pacing and structured training planning.
About this calculator
The power-duration curve models how peak sustainable power declines as effort length increases. For short efforts (up to 60 seconds), anaerobic energy systems dominate: P = (FTP + W′ / duration) × fatigueLevel, where W′ is your anaerobic work capacity in joules. For efforts between 1 minute and 1 hour, aerobic fatigue sets in with a mild decay: P = FTP × (duration / 3600)^(−0.05) × fatigueLevel. For efforts beyond one hour, the decay steepens: P = FTP × (duration / 3600)^(−0.07) × fatigueLevel. FTP (Functional Threshold Power) is the highest average power sustainable for approximately one hour; it anchors the entire curve. The fatigue level scalar (≤1.0) adjusts all outputs when you are carrying accumulated training load or fatigue, making predictions more realistic for real-world conditions.
How to use
Assume FTP = 250 W, anaerobic capacity (W′) = 18,000 J, fatigue level = 0.95, and target duration = 30 seconds. Since 30 ≤ 60, use the short-effort formula: P = (250 + 18,000 / 30) × 0.95 = (250 + 600) × 0.95 = 850 × 0.95 = 807.5 W. Now try a 2-hour ride (7,200 s): P = 250 × (7200 / 3600)^(−0.07) × 0.95 = 250 × 2^(−0.07) × 0.95 = 250 × 0.9527 × 0.95 ≈ 226 W. These outputs guide effort targets for intervals and endurance pacing.
Frequently asked questions
What is FTP and how do I measure it accurately for this calculator?
Functional Threshold Power (FTP) is the highest average power you can sustain for roughly 60 minutes, and it is the cornerstone of cycling performance modelling. The most common field test is a 20-minute maximal effort; multiply the average power by 0.95 to estimate FTP. Alternatively, a ramp test — increasing power by a fixed watt increment each minute until failure — estimates FTP as roughly 75% of the peak 1-minute power achieved. Lab-based lactate threshold testing is the gold standard but rarely practical. Re-test every 6–8 weeks as fitness changes to keep the calculator's outputs meaningful.
How does anaerobic work capacity (W prime) affect my short-duration power estimates?
W′ (W prime) represents the finite reservoir of anaerobic energy available above FTP before exhaustion. A larger W′ means you can sustain very high power for longer during sprints and short attacks. In the formula, W′ is divided by duration in seconds, so its influence diminishes rapidly beyond 60–90 seconds as aerobic metabolism takes over. Typical W′ values range from 10,000 J for lighter climbers to 25,000 J or more for powerful sprinters. You can estimate W′ from two or more maximal efforts of different durations using the critical power model.
Why does sustainable power drop for longer cycling efforts even when I feel fresh?
As effort duration increases, the body increasingly relies on fat oxidation and must carefully regulate heat, glycogen, and cardiovascular strain — all of which limit how hard you can push. The power-duration relationship follows a hyperbolic decay; the exponents −0.05 (for 1–60 min) and −0.07 (beyond 60 min) capture this well-documented drop-off in human performance data. Even elite athletes see a meaningful reduction in power from their 5-minute peak to their 4-hour average. Pacing strategies that ignore this curve lead to early fatigue, while those aligned with it allow optimal energy distribution across the full effort.