TSS calculator
Calculate the Training Stress Score of a ride from duration, normalized power and FTP. One number for the session load.
Everything is computed in your browser — the values you enter are never sent or stored.
Result
- TSS
- 128
- IF (Intensity Factor)
- 0.80
- Interpretation
- Low load — usually recovered by the next day.
TSS describes a single session. Judging fitness and fatigue needs a series of days — see CTL, ATL and TSB.
How we calculate this
- IF = NP / FTP
- TSS = (seconds × NP × IF) / (FTP × 3600) × 100
- Simplified: TSS = hours × IF² × 100
The formulas come from the app’s domain specification and are covered by unit tests. The same code powers zones inside the app.
Want these numbers to feed your plan automatically?
In the app, zones update after every test and the plan adapts to your data and how you feel.
This calculator is informational and does not replace a doctor, physiotherapist or coach. Results based on population formulas are estimates, not measurements. Read the full disclaimer →