Training Stress Score (TSS) Calculator
Estimate the training stress of a session from its duration, intensity and your threshold power — the workload metric behind fatigue and fitness tracking.
How it works
IF = NP ÷ FTP · TSS = (duration_sec × NP × IF) ÷ (FTP × 3600) × 100 = hours × IF² × 100
Training Stress Score, popularised by TrainingPeaks, rolls duration and intensity into one number so you can compare a short hard session with a long easy one. One hour at exactly your threshold (FTP) is defined as 100 TSS. Because it squares the intensity factor, going harder raises stress much faster than going longer — a useful reminder that intensity is expensive.
Worked example
A 60-minute ride averaging 200 W with a 250 W FTP gives IF = 200 ÷ 250 = 0.80. TSS = 1 hour × 0.80² × 100 = 64. A full-hour threshold effort (IF 1.0) would be 100.
Frequently asked questions
What counts as a big TSS day?
Roughly: under 50 is easy and recovers overnight, 50–150 is moderate, 150–300 is hard with residual fatigue, and above 300 is an epic day needing several days to absorb. These are guides, not rules.
Can I use this for running?
This power-based form is designed for cycling. Running has an analogous rTSS based on pace versus threshold pace, but the inputs differ — use a pace-based tool for runs.
What is normalised power?
Normalised power weights the surges in a ride so a variable effort is not flattered by its average. If you only have average power, entering it gives a reasonable approximation for steady rides.
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This calculator is for educational purposes. Double-check important results before acting on them.