TSS Calculator

Training Stress Score (TSS) combines how hard and how long you rode into a single number. It was developed by Andrew Coggan as part of the power-based training framework and is now the standard unit for quantifying session workload in cycling.

A TSS of 100 roughly equals a one-hour ride at exactly your Functional Threshold Power (FTP). Ride harder than threshold and TSS accumulates faster per hour. Ride below threshold and it accumulates slower.

TSS is most useful when you track it across a week or a training block. Individual session scores help you classify ride difficulty, but the real value comes from managing weekly totals to balance adaptation and recovery.

TSS depends on three inputs: ride duration, Normalized Power (NP), and your current FTP. The Intensity Factor (IF) is the ratio of NP to FTP, and it tells you how intense the ride was relative to your threshold.

The formula uses NP rather than average power because NP better captures the metabolic cost of variable-intensity riding. Two rides with the same average power can have very different physiological costs if one included repeated surges.

Per-session TSS is most useful when mapped to recovery expectations. Coggan's framework provides rough categories, but individual response varies with fitness level, nutrition, sleep quality, and accumulated fatigue from prior days.

Low TSS sessions (under 60) are generally recoverable within a day. Sessions between 60 and 120 create meaningful training stimulus without deep fatigue for most trained cyclists. Scores above 150 are typically reserved for race days, hard group rides, or deliberate overreaching blocks.

Weekly TSS totals provide a better picture than daily scores. Most recreational cyclists accumulate 300-500 TSS per week. Competitive amateurs might sustain 500-700. Professional cyclists can exceed 800-1000 during heavy training blocks, supported by optimised recovery protocols.

IF tells you how hard a ride was relative to your threshold. It is particularly useful for pacing time trials and gauging race effort retrospectively.

For a well-paced 40 km time trial, IF typically falls between 0.95 and 1.05. Long endurance rides usually sit between 0.60 and 0.75. If a planned recovery ride shows IF above 0.70, you are riding too hard for the intended adaptation.

IF is also the fastest way to spot an outdated FTP. If you consistently ride at IF 1.05+ for durations that should be at threshold, your FTP has likely improved and needs retesting.

The most frequent error is using average power instead of Normalized Power. On a ride with lots of coasting and surges, average power can understate NP by 10-25%. This makes the calculated TSS lower than the actual physiological cost.

A second common mistake is treating TSS as the only recovery indicator. TSS does not account for environmental heat stress, eccentric muscle damage from climbing, or psychological fatigue. Use it alongside perceived exertion and heart-rate decoupling data.

Finally, TSS accuracy depends entirely on your FTP being current. An outdated FTP inflates or deflates every TSS value downstream. Retest every 4-8 weeks during structured training.