Training Stress Score Calculator
TSS and Intensity Factor for any cycling or running session
Training load (TSS)
Training Stress Score and Intensity Factor for any session.
How the TSS calculator works
Training Stress Score puts a number on how much a session cost. It combines duration with intensity relative to your threshold: TSS = (seconds × NP × IF) ÷ (FTP × 3600) × 100, where IF, the intensity factor, is normalized power divided by FTP. One hour exactly at FTP scores 100; an easy two-hour ride and a hard forty-minute session can score the same.
Enter the duration, the normalized (or average) power and your FTP and the calculator returns IF and TSS with a label for the load. Under 150 a session is usually absorbed by the next day; 150–300 leaves some fatigue into the next one; 300–450 lingers for two days; above 450 needs several days.
Summed over days, TSS drives the fitness–fatigue model: CTL, the 42-day average, is your fitness; ATL, the 7-day average, your fatigue; and TSB, the difference, your form. LaChart calculates all three from every synced ride and run.
Questions
- What is a good weekly TSS?
- It depends on what you can absorb. Recreational riders sit around 300–500 a week, serious amateurs 500–800, professionals well above 1000. A ramp of more than 5–8 CTL points a week is where injury and illness start to appear.
- What about running or sessions without power?
- Running uses rTSS from pace against threshold pace, and any sport can use hrTSS from heart rate against threshold heart rate. The scale is the same — an hour at threshold is 100 — so the sports add up in one load.
- Why does TSS use normalized rather than average power?
- Because a variable ride costs more than its average suggests. Normalized power weights the hard moments the way the body feels them, so an interval session with a low average still scores as the hard session it was.
Ready to track your full training load?
LaChart combines lactate testing, training analytics, Strava and Garmin sync and coach collaboration in one place.
