TSS (Training Stress Score) Calculator

Frequently Asked Questions

How is TSS calculated?

TSS = (duration_seconds × Normalized Power × Intensity Factor) ÷ (FTP × 3600) × 100. A 1-hour ride at FTP (IF = 1.0) equals exactly 100 TSS by definition.

What TSS values are typical?

Easy hour ≈40–55 TSS, tempo hour ≈70–85, threshold hour ≈90–100, race ≈100–180. Weekly totals: 200–400 for fitness riders, 500–800 for serious amateurs, 900–1,400 for pros (with care).

How does TSS feed CTL/ATL/TSB?

CTL (Chronic Training Load) is a 42-day exponentially weighted average of TSS - your fitness. ATL (Acute) is 7-day weighted - fatigue. TSB = CTL − ATL is form: −10 to −30 means hard training, +5 to +15 is race-ready.

Can I use TSS without a power meter?

Yes - hrTSS and rTSS use heart rate or pace instead. They're less precise (HR lags effort, drifts with heat) but still useful for tracking load. Pair with RPE for sanity checks.

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This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

Training Stress Score (TSS) is the industry-standard single number for how hard a ride was, designed by Dr Andy Coggan to roll duration, intensity and your personal threshold into one comparable figure. An hour spent exactly at FTP is defined as 100 TSS. Anything easier or shorter scores less; anything harder or longer scores more. This calculator takes your ride duration, the ride's Normalised Power (NP) reported by your head unit or analysis platform, and your current FTP, then returns TSS along with the Intensity Factor (IF) used in the calculation and a plain-English recovery hint.

Formula / Method

TSS = (duration_sec × NP × IF) ÷ (FTP × 3600) × 100, where IF = NP ÷ FTP. Because IF already contains NP/FTP, the formula simplifies to TSS = (duration_hours) × IF² × 100. The quadratic on IF is the reason a one-hour Z2 ride at IF 0.65 scores only 42 TSS, while a one-hour threshold effort at IF 1.0 scores 100 - intensity matters far more than duration in the medium term. Weekly TSS totals (Chronic Training Load, CTL) build the fitness curve in most coaching software, and the difference between recent (ATL) and chronic load drives the Training Stress Balance - the "form" meter.

Worked Example

A 2-hour ride with NP = 220 W against an FTP of 250 W. IF = 220 ÷ 250 = 0.88. Duration = 7,200 s. TSS = (7,200 × 220 × 0.88) ÷ (250 × 3,600) × 100 = 1,393,920 ÷ 900,000 × 100 ≈ 155 TSS. Cross-check with the simpler form: 2 hours × 0.88² × 100 = 2 × 0.7744 × 100 = 154.9 TSS - matches. This ride sits squarely in the "sweet spot" band and would typically need about 36 hours of easier riding before peak quality work returns.

Common Mistakes

Using average power instead of normalised power; surgy rides will under-report TSS by 10–20%.

Forgetting to update FTP. After an FTP bump the same ride suddenly produces a lower TSS - that's mathematically correct but coaches usually re-baseline.

Comparing TSS across sports without sport-specific FTPs (running rTSS uses pace, swimming sTSS uses CSS - not interchangeable).

Treating weekly TSS targets as universal: 600 TSS/week destroys a beginner and bores a Cat 1.

Ignoring TSS from indoor sessions with no cooling - same number, much greater physiological cost.

Tips & FAQ

Typical weekly TSS? Casual rider 200–400, club racer 500–800, amateur national level 800–1,200, grand tour pros 1,500–2,000+ in build blocks. Daily caps? Anything over 250 TSS is a hard day; over 350 TSS usually requires the next day easy. How does TSS relate to calories? Roughly 1 TSS ≈ 10–12 kcal of carbohydrate cost for trained riders - useful for fuelling. Why use NP and not average? Average power treats one minute at 400 W the same as one minute at 0 W; NP applies a 30-second rolling fourth-root weighting that better matches metabolic cost, so 100 TSS at constant power and 100 TSS done as intervals impose roughly equal training stress. What if I don't have a power meter? Use hrTSS (heart-rate-based) or RPE TSS in Training Peaks - less accurate, still useful.

TSS (Training Stress Score) Calculator

Frequently Asked Questions

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