TSS Calculator: Training Stress Score & Weekly Load

How the TSS calculator works

Training Stress Score quantifies how much a workout costs you in terms of recovery. The formula, introduced by Andrew Coggan, is TSS = (duration in hours × IF²) × 100, where Intensity Factor (IF) is the ratio of normalized power to FTP. A one-hour workout at FTP is 100 TSS by definition.

For each workout, estimate the IF: a recovery ride is around 0.55, endurance is 0.65 to 0.75, tempo is 0.80 to 0.85, sweet spot to threshold is 0.88 to 0.95, VO2max intervals average 0.95 to 1.05 across the whole session. Duration × IF² × 100 gives the TSS.

Weekly TSS is the sum across all workouts in a 7-day window, a value most coached athletes know by heart. For untrained cyclists, 300 weekly TSS is a meaningful block; for experienced amateurs in build phase, 600–900 is typical; for serious age-group athletes in peak weeks, 1,000 to 1,400 is realistic.

CTL (Chronic Training Load) is an exponentially weighted average of daily TSS over the last 42 days, your fitness proxy. ATL (Acute Training Load) is the same thing over the last 7 days, your fatigue proxy. TSB (Training Stress Balance) is CTL minus ATL: positive means fresh, negative means loaded.

The simplified preview here assumes you are starting at zero and adding one week of training on top. It is not a substitute for the full 42-day rolling calculation TrainingPeaks does, but it gives you a useful sense of whether a week of planned training is heavy, moderate, or light relative to your history.

TSS = (hours × IF²) × 100 · IF = NP ÷ FTP