Training Stress Calculator (TSS)
Calculate TSS from power, duration, and FTP.
How We Calculate This
Power TSS = (Duration in seconds × NP × IF) / (FTP × 3600) × 100, the model defined by Dr Andrew Coggan. Normalised Power (NP) accounts for intensity variability and Intensity Factor (IF) = NP / FTP. If only average power is available, it is used in place of NP. One hour at FTP equals 100 TSS.
Heart-rate TSS estimates intensity from heart-rate reserve (Karvonen): IF = (average HR − resting HR) / (threshold HR − resting HR), then TSS = hours × IF² × 100. This anchors easy rides correctly instead of inflating them with a raw average-to-threshold ratio.
RPE TSS maps your session effort (Borg CR10) to an approximate IF and uses the same hours × IF² × 100 form. Use power when you have it — it is the most accurate.
Frequently Asked Questions
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TSS Calculator
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Last updated: March 2026
All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.