TSS Calculator: free training stress score calculator.
Enter how long you rode, your normalized power and your FTP. Get your Training Stress Score and Intensity Factor.
Training Stress Score
128TSS
The same stress as 1 h 17 min at your FTP. One hour at FTP is 100 TSS by definition.
Allen and CogganIntensity Factor
0.80IF
Your normalized power was 80% of your FTP: Coggan's level 3, tempo.
Allen and CogganCoggan levelsTSS grows with time and with the square of intensity. 2 h at IF 0.80 scores 128; the same ride at IF 0.85 would score 145.
How much a score takes out of you depends on your fitness and your week. Your AI can read it against your recent load.
Hand it to your AI
Your AI can check these numbers against your training and adjust them. The prompt has your results filled in.
See the prompt
I rode 2 h at a normalized power of 200 W. My FTP is 250 W. That is an IF of 0.80 and a TSS of 128 (Allen and Coggan's formula), the same stress as 1 h 17 min at FTP. Look at my training load over the last six weeks and tell me how this ride fits: what my next few days should look like, and whether my FTP needs a retest.
Gemini, Grok Bot, Dots, Muse and Cue: copy the prompt and paste it in.
With Memory.fit, your AI would already know your training load.
On Android now: get it on Google Play. One email when the iPhone app is on the App Store.
How it works
How the TSS Calculator works.
Training Stress Score, or TSS, puts one number on how hard a ride was, counting both how long and how intense. Andrew Coggan and Hunter Allen built it.
It starts with Intensity Factor, or IF: your normalized power divided by your FTP. Normalized power is the steady power that would have cost your body the same as the ride you actually did, surges and all. Your bike computer or training app gives it to you.
TSS multiplies your time by your normalized power and your IF, then scales it so that one hour at exactly your FTP scores 100. Because IF counts twice, intensity weighs more than time: two hours at IF 0.80 score 128, while two hours at IF 0.90 score 162.
A score is not good or bad on its own. What a 150 does to you depends on your fitness and the rest of your week. That is why the number is most useful next to your recent load, which is something your AI can read for you.
If you score more than 100 an hour for longer than an hour, check your FTP. FTP is about the most you can hold for an hour, so it is probably set too low.
The formula
- IF = NP ÷ FTP
- TSS = (seconds × NP × IF) ÷ (FTP × 3,600) × 100
- which is the same as hours × IF² × 100
The science
Where the numbers come from.
Every number on this page links to the paper it comes from. How Memory.fit uses the science
Allen H, Coggan AR, McGregor S. Training and Racing with a Power Meter. 3rd edition. VeloPress, 2019. ISBN 978-1-937715-93-9.
Book · 2019
Friel J. Estimating Training Stress Score (TSS). TrainingPeaks, September 21, 2009, updated 2026.
Article · 2009 · Read it
Coggan AR. Cycling Power Zones Explained (Power Training Levels). TrainingPeaks, 2016, updated 2026.
Article · 2016 · Read it
Example
A worked example.
A cyclist with an FTP of 250 W who rides 2 hours at a normalized power of 200 W.
- 1IF = 200 ÷ 250 = 0.80. Normalized power at 80% of FTP sits in Coggan's level 3, tempo.
- 2TSS = (7,200 × 200 × 0.80) ÷ (250 × 3,600) × 100 = 128.
- 3That is the same stress as 1 h 17 min at FTP, since one hour at FTP is 100.
Questions
TSS Calculator: questions.
There isn't one. TSS counts how much stress a ride carried, and what that does to you depends on your fitness and the rest of your week. Read it next to your recent load, not on its own.
IF is how hard the ride was compared with your FTP, whatever its length. TSS adds the time: a short hard ride and a long easy one can score the same TSS with very different IF.
Because surges cost more than their average shows. Normalized power weighs the hard parts more, so a ride full of attacks scores higher than a steady ride at the same average.
Only if you rode above your FTP for it. FTP is about the most you can hold for an hour, so 100 TSS an hour is the ceiling for anything longer. A long ride scoring higher means your FTP is set too low.
This formula needs power and an FTP, so it is for cycling, or for running with a power meter and a running FTP.
Not medical advice. These numbers come from published research on groups of athletes. Your own needs can differ; talk to a doctor or a sports dietitian about any health condition.