How to Calculate TSS in Cycling

By WattWorks · April 13, 2026 · 9 min read

Training Stress Score (TSS) is the single most important metric for training planning in cycling. It combines intensity and duration into one number — making completely different sessions directly comparable.

    Short definition: TSS measures how much training stress a session places on your body. One hour at exactly FTP power always equals 100 TSS — regardless of your absolute FTP value.
  

What is TSS (Training Stress Score)?

TSS was developed by Andrew Coggan and is based on two factors: the duration of a ride and the Intensity Factor (IF) — the ratio of Normalized Power (NP) to your FTP.

The key insight: TSS is normalised. One hour at exactly FTP power always equals 100 TSS — for a rider with FTP 200 W just as for one with FTP 350 W. This makes TSS values comparable across riders and sessions.

The TSS Formula

IF (Intensity Factor) = NP / FTP TSS = (Duration in seconds × NP × IF) / (FTP × 3600) × 100 Simplified: TSS = Hours × IF² × 100

Example: 3-hour Zone 2 ride

FTP = 250 W NP = 175 W (70% FTP, Zone 2) IF = 175 / 250 = 0.70 TSS = 3 × 0.70² × 100 TSS = 3 × 0.49 × 100 = 147 TSS

Example: 1-hour threshold intervals

FTP = 250 W NP = 237 W (95% FTP, threshold zone) IF = 237 / 250 = 0.95 TSS = 1 × 0.95² × 100 TSS = 1 × 0.9025 × 100 = 90 TSS

Although the interval session is shorter, it generates almost as much stress — because of the higher intensity.

Typical TSS Values for Different Sessions

Session	Duration	Intensity	TSS (approx.)
Easy recovery ride	1h	Z1 (55% FTP)	30
Zone 2 endurance	2h	Z2 (65% FTP)	85
Long Zone 2 ride	4h	Z2 (65% FTP)	170
Threshold intervals	1.5h	Z4 (95% FTP)	135
FTP test (60 min)	1h	100% FTP	100
Hard race	3h	85% FTP	217
Grand Tour stage (pro)	5h	75% FTP	281

What is a good TSS per week?

TSS/Week	Volume	Typical Profile
150–250	Low	Beginner, returning rider, recovery week
250–400	Moderate	Recreational cyclist, 5–8h/week
400–600	High	Ambitious amateur, 8–12h/week
600–900	Very high	Competitive racer, training camp
> 900	Pro level	Professionals, stage races

TSS and Recovery

TSS helps not just with planning, but also with recovery. As a rule of thumb:

< 150 TSS — full recovery possible within 24h
150–300 TSS — 24–48h recovery
300–450 TSS — 48–72h recovery
> 450 TSS — several days; a recovery week is recommended

What is the Intensity Factor (IF)?

IF Range	Intensity	Session Type
< 0.60	Very easy	Active recovery
0.60–0.75	Aerobic/Z2	Endurance base
0.75–0.85	Tempo/Z3	Group rides
0.85–0.95	Lactate threshold/Z4	Threshold intervals
0.95–1.05	FTP zone	Time trials, FTP test
> 1.05	Anaerobic	VO2max intervals, races

Calculating TSS without a power meter

If you don't have a power meter, TSS can be estimated from heart rate data — known as hrTSS (heart rate TSS). Accuracy is lower, but sufficient for planning and orientation.

Apps like WattWorks calculate TSS automatically from your FIT files, Strava data, or heart rate.

    Important: TSS is always relative to your personal FTP. If your FTP changes, all historical TSS values change retroactively. Keep your FTP current — WattWorks does this automatically via eFTP.
  

Calculate TSS automatically with WattWorks

WattWorks calculates TSS, IF and NP automatically after every upload — from FIT files or Strava. Plus automatic CTL/ATL/TSB tracking and AI-based training planning.

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Frequently asked questions about TSS

How much TSS per week is reasonable?

For recreational cyclists training 5–8 hours per week, 300–500 TSS per week is realistic and appropriate. More important than the absolute value is consistency over weeks and months.

What is Normalized Power (NP)?

Normalized Power (NP) is a mathematically calculated power value that better reflects the metabolic cost of variable power output (such as during intervals or climbs) than average power alone. NP is always ≥ average power.

Can TSS be more than 100 per hour?

Yes — if you ride above your FTP (IF > 1.0), TSS increases accordingly. At IF 1.1 for 1 hour, TSS is 121. In races or VO2max intervals, TSS > 100/h is possible.

Why is TSS so high after a long Zone 2 ride?

TSS scales quadratically with IF and linearly with duration. Long sessions accumulate significant TSS even at low intensity. A 5-hour Zone 2 ride (IF 0.65) yields approximately 211 TSS — more than most 1-hour intensity sessions.

What happens if my FTP is set incorrectly?

An FTP set too low overestimates TSS (all sessions appear more intense than they are); an FTP set too high underestimates TSS. A current and correct FTP value is therefore critical for TSS accuracy.