TSS calculator
Enter how long you rode, the normalized power (NP) of the ride and your functional threshold power (FTP). The calculator gives the Intensity Factor and the Training Stress Score, the load numbers cycling platforms use to plan training.
Runs in your browser: nothing you enter is sent anywhere.
How to use
- Enter the ride duration in hours and minutes.
- Enter the normalized power of the ride and your current FTP, both in watts.
- Read TSS and IF; the third number shows how much TSS one hour at this intensity adds.
- IF = NP ÷ FTP
- TSS = (seconds × NP × IF) ÷ (FTP × 3600) × 100 = hours × IF² × 100
Because IF is squared, intensity raises the load quickly: an hour at IF 0.7 is 49 TSS, an hour at IF 0.9 is 81.
Example
A 2-hour ride at NP 200 W with an FTP of 250 W:
- IF = 200 ÷ 250 = 0.8;
- TSS = 2 × 0.8² × 100 = 128;
- one hour at this intensity adds 64 TSS.
Tips
- Re-test FTP every 6–8 weeks or after a training block; the FTP calculator works from 20-minute or ramp tests.
- Weekly TSS is a simple way to compare training load between weeks.
- TSS describes the load, not its type: 100 TSS of easy endurance and 100 TSS of intervals train different things.
Frequently asked questions
How is TSS calculated?
TSS = (seconds × NP × IF) ÷ (FTP × 3600) × 100, with IF = NP ÷ FTP. This simplifies to hours × IF² × 100. Two hours at NP 200 W with FTP 250 W: IF = 0.8, TSS = 2 × 0.64 × 100 = 128.
What is a high TSS?
One hour flat out at threshold is 100 by definition. As a rough guide, rides under 150 are usually recovered from by the next day, 150–300 can leave fatigue into the day after, and above 300 may take several days. Your own fitness changes these limits.
Why does it use normalized power instead of average power?
Hard efforts cost more than their share of the average: a ride of sprints and coasting feels harder than steady riding at the same average watts. Normalized power weighs those surges, so TSS reflects the real load. Your bike computer or training app shows NP for each ride.
What if I do not know my NP?
For a steady ride, average power is close to NP and gives a fair estimate. For group rides or intervals, average power underestimates the load. Keep your FTP current too — an FTP set too low inflates every TSS.