Running Stress Score Calculator
A power-based running stress score reduces a whole run to one training-load number by combining how hard you ran (intensity) with how long you ran (duration). It follows the established Training Stress Score logic: one hour held exactly at your critical power equals 100 points. This calculator takes your average running power, your personal critical power, and the run duration, computes your intensity factor, and returns the stress score on that 100-per-threshold-hour scale. Because critical power is individual and changes with fitness, it is a user-editable input rather than an assumed figure.
Running stress score formula
Intensity factor (IF) = average power / critical power
Duration in seconds = minutes * 60
Stress score = (seconds * average power * IF) / (critical power * 3600) * 100
One hour held at critical power gives intensity factor 1.0 and a stress score of 100. The score rises with both higher intensity and longer duration, so it captures the full training load of the session.
Interpreting your stress score
- Under 50 points: a light session that typically needs little recovery.
- 50 to 100 points: a moderate session, common for steady aerobic running.
- 100 to 150 points: a hard session, often a long run or tempo workout.
- Above 150 points: a very demanding session that usually requires extra recovery.
- The U.S. Centers for Disease Control and Prevention recommends balancing higher-intensity activity with adequate recovery.
Running stress score: frequently asked questions
What is a running stress score?
A running stress score is a single number that summarizes the training load of a run by combining its intensity and duration. It is built from the same logic as the cycling Training Stress Score: a one-hour effort at your threshold (critical power) is defined as 100 points. Longer or harder runs score higher; shorter or easier runs score lower.
How is the stress score calculated?
Stress score equals duration in seconds times average power times intensity factor, divided by critical power times 3,600, multiplied by 100. Intensity factor is your average power divided by your critical power. The 3,600 is the number of seconds in one hour, which anchors the scale so that one hour at critical power equals exactly 100 points.
What is critical power?
Critical power is the highest running power you can sustain for roughly an hour, often estimated from a hard test effort. It plays the role of a threshold. Because it is personal and changes with fitness, this calculator takes it as a user-editable input rather than assuming a value.
What counts as a high stress score?
Roughly, a score under 50 is a light session, 50 to 100 is moderate, 100 to 150 is hard, and above 150 is very demanding and usually needs extra recovery. These bands are guidelines, not rules; what matters is tracking your own weekly accumulation and how you recover from it.
Why use power instead of pace for training load?
Running power responds immediately to hills, wind, and surface, whereas pace does not. A steady effort up a hill shows roughly constant power but slowing pace. Basing stress on power therefore reflects the true physiological demand of the run more faithfully than pace-based load on varied terrain.
Official sources
- U.S. Centers for Disease Control and Prevention: Physical Activity.
- USA Track & Field: coaching and training resources.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.