Training Stress Score (TSS) Calculator

Understanding the Training Stress Score — concept and principle

Training Stress Score (TSS) puts a single number on how hard a ride was, combining intensity and duration. Developed by Andrew Coggan for power-meter training, it lets you compare a short hard interval session with a long easy ride and add workouts up into weekly load. This calculator needs your normalized power, your FTP and the ride's duration.

Block width is time and height is intensity squared; the area is the TSS.

How it is calculated

Intensity factor (IF) = normalized power (NP) ÷ FTP.
TSS = (seconds × NP × IF) ÷ (FTP × 3600) × 100.

Because NP ÷ FTP is IF, the formula simplifies to TSS = hours × IF² × 100. One hour at exactly FTP gives IF = 1 and TSS = 100.

The principle

Normalized power is a weighted average that estimates the physiological cost of a variable ride: it takes 30-second rolling averages of power, raises them to the fourth power, averages them and takes the fourth root, so surges count more than steady riding. Dividing by FTP makes intensity personal, because 220 W is easy for one rider and hard for another. Intensity appears squared because harder efforts drain the body more than proportionally, while duration is linear. Scaling to 100 for one hour at threshold gives an intuitive reference point.

Worked example

NP 220 W, FTP 250 W, 90 minutes.

IF = 220 ÷ 250 = 0.88.
Duration = 90 × 60 = 5,400 s.
TSS = (5,400 × 220 × 0.88) ÷ (250 × 3,600) × 100 = 116.16 → 116.
Check: 1.5 h × 0.88² × 100 = 1.5 × 0.7744 × 100 = 116.16.

Each point is the calculator re-run with only “FTP (W)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

FTP (W)	TSS
62.5	1,859
125	465
188	207
250	116
312	74
375	52
500	29

How to read the result

Where does your result fall?

A commonly used guide from Coggan's work: below about 150 is a low load, usually recovered from by the next day; 150–300 is medium, with some fatigue the next day; 300–450 is high; and above 450 is very high, with fatigue that can last several days. An IF around 0.75 or lower is endurance riding, 0.85–0.95 is typical of tempo to threshold work or a hard group ride, and about 1.0 or more is race intensity for an hour or less. Daily TSS values also feed the chronic training load (a 42-day average) and acute load (7-day average) used to manage fitness and fatigue.

Common mistakes

Entering average power instead of normalized power.
Using an outdated FTP; if FTP is set too low, TSS is inflated.
Comparing TSS between different riders as if it measured absolute work.
Adding running or heart-rate-based scores without noting they are estimates on a different basis.

Keep in mind: TSS is a model of training load, not a measure of health or recovery status. Sleep, illness and life stress also affect how you respond, so use it alongside how you feel.

Frequently asked questions

Is a TSS of 100 always one hour at FTP?

Not necessarily. Two hours at IF 0.71 also gives about 100, because 2 × 0.71² × 100 ≈ 101.

Can IF be above 1?

Yes, for efforts shorter than an hour, such as a time trial or criterium, NP can exceed FTP.

How is TSS different from heart-rate TRIMP?

Both combine intensity and time. TSS uses power relative to FTP; TRIMP uses heart rate, which lags behind changes in effort and drifts with heat and fatigue.

Sources: Allen H, Coggan A. Training and Racing with a Power Meter. VeloPress.

Checked 8 Nov 2026. Published formulas cited on the page. For information only — not medical advice.

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