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Easily calculate your fatigue index with our accurate Fatigue Index Calculator. Learn the formula, what’s a good score, and how to interpret your results.
Fatigue is a natural part of any intense physical activity. Whether you are a sprinter, cyclist, or athlete performing anaerobic training, your performance drops over time. The fatigue index tells you exactly how quickly your power declines. Our Fatigue Index Calculator helps you measure this drop with accuracy so you can monitor your performance and improve over time.
The fatigue index is a percentage that shows how much your power output decreases during a high-intensity, short-duration exercise. It is most commonly measured during anaerobic tests such as the Wingate test. The higher the fatigue index, the greater your loss of power over the test period. This number reflects your ability to maintain peak performance and resist fatigue.
The calculation is straightforward and uses this formula:
Fatigue Index (%) = (Peak Power − Lowest Power) ÷ Peak Power × 100
Peak Power is the highest power output you can produce, usually in the first few seconds of the test. Lowest Power is the smallest power value recorded towards the end. The result is shown as a percentage.
Example: If your peak power is 800 W and your lowest power is 320 W:
FI = (800 − 320) ÷ 800 × 100 = 60%
This means your power dropped by 60% during the test.
A good fatigue index depends on your sport and training level. Lower scores are better because they show you can maintain high power for longer. Athletes with excellent anaerobic endurance often have a fatigue index below 30%. Recreational athletes may have a score between 45% and 60%, while scores above 60% suggest a need for targeted endurance training.
In almost every case, a lower fatigue index is preferred. A low score means your body can sustain performance under pressure, while a high score means you lose power quickly. For competitive sports, maintaining peak performance is crucial, so reducing your fatigue index should be a training goal.
Using our online calculator is simple. Enter your peak power and lowest power values. You can select the unit of measurement, such as watts, watts per kilogram, horsepower, or kilogram-meters per minute. If you are using watts per kilogram, you will need to enter your body mass as well. The calculator will instantly convert your data into watts, run the fatigue index formula, and display your result with a clear interpretation.
The fatigue index is one of the best tools for measuring your short-term endurance and power maintenance. It’s widely used in sports science and by athletes looking to track progress. With our Fatigue Index Calculator, you can quickly find out where you stand and what needs improvement. The goal is always to train smart and work towards a lower fatigue index for better performance.
It is a percentage showing how much your power drops during high-intensity exercise.
Use the formula: (Peak Power − Lowest Power) ÷ Peak Power × 100.
Below 30% is excellent, 30–45% is good, 45–60% is average, and above 60% means you need endurance improvement.
Lower is better because it shows you can maintain high performance for longer.
Yes, it works for cycling, running, sprinting, and any sport that measures peak and lowest power output.