Calculator Inputs
Use the responsive form below. It shows three columns on large screens, two on medium screens, and one on mobile.
Example Data Table
Use these sample sessions to understand how duration and intensity shift the final training stress score.
| Session | Duration | Normalized Power (W) | FTP (W) | Intensity Factor | TSS |
|---|---|---|---|---|---|
| Tempo Build | 01:15:00 | 230 | 280 | 0.821 | 84.20 |
| Threshold Repeats | 00:55:00 | 265 | 280 | 0.946 | 82.10 |
| Long Endurance | 02:30:00 | 190 | 280 | 0.679 | 115.30 |
| VO2 Block | 00:45:00 | 300 | 280 | 1.071 | 86.10 |
Formula Used
The calculator applies common performance modeling formulas based on duration, threshold, and power-derived intensity.
1) Training Stress Score
TSS = (Seconds × NP × IF ÷ (FTP × 3600)) × 100
2) Intensity Factor
IF = NP ÷ FTP
3) Variability Index
VI = NP ÷ Average Power
4) Work in Kilojoules
Work (kJ) = Average Power × Seconds ÷ 1000
How to Use This Calculator
Follow these steps to calculate a session score, interpret intensity, and export your final summary.
Step 1
Enter FTP and total session duration first. These fields establish the threshold reference and the time base for the score.
Step 2
Enter normalized power if you have it. If not, provide a manual intensity factor instead. Average power is optional but helpful.
Step 3
Add distance, weight, elevation, cadence, and notes if you want more context such as speed, climbing rate, and watts per kilogram.
Step 4
Press the calculate button. Your results appear above the form, directly below the header, along with the Plotly comparison chart.
Step 5
Use the CSV or PDF buttons to save your summary for reporting, session review, coaching notes, or engineering-style performance tracking.
FAQs
These quick answers explain how the score works and how to interpret the output.
1. What is training stress score?
TSS estimates overall workload by combining duration and intensity into one score. It helps compare short hard sessions with longer moderate efforts using a common scale.
2. Why does the formula use normalized power?
Average power can hide surges and recoveries. Normalized power reflects physiological cost better, so it describes real session strain more accurately than a simple mean.
3. What is a strong daily TSS value?
It depends on training history, recovery, and season goals. Many athletes manage 30 to 80 well, while 100 or more often feels demanding.
4. Can I use manual intensity factor instead?
Yes. If you already know intensity factor, enter it and leave normalized power blank. The calculator can estimate normalized power from FTP and IF.
5. What does variability index show?
Variability index equals normalized power divided by average power. Values near 1.00 suggest steady pacing, while higher values indicate more surging and uneven effort.
6. Does distance directly change TSS?
No. TSS is mainly driven by time and intensity. Distance still helps explain speed, route difficulty, and efficiency when you review the session.
7. Is this useful for indoor sessions?
Yes. Indoor workouts often provide cleaner power data, which makes TSS especially useful for comparing intervals, endurance blocks, and recovery sessions.
8. How should I use very high TSS days?
Pair high-load days with recovery planning, lighter follow-up work, nutrition, and sleep. Repeating very high TSS too often can reduce quality and increase fatigue.