About the TRIMP Calculator
This TRIMP calculator works out Banister's training impulse, a single number that combines how long you trained with how hard your heart was working. Enter the session duration, your average heart rate, your resting and maximum heart rate, and your sex, and it returns the TRIMP score, the fraction of heart-rate reserve you used and the load per hour.
TRIMP is the original heart-rate based training-load metric, and it underpins many of the load scores in modern watches and apps. It is useful for runners, cyclists, rowers and team-sport athletes who train with a heart-rate monitor but not a power meter, and for anyone who wants to add up the load of different sessions over a week.
Because the weighting rises exponentially with intensity, a hard 45 minutes can carry more load than an easy 90. The formula uses average heart rate for the whole session, so intervals with big swings are slightly under-weighted; for those, calculating each block separately and adding them gives a closer answer.
With the default inputs, the trimp is 104.4. Change any value above to recalculate instantly.
How to use the trimp calculator
- 1Choose your sex (the weighting constants differ).
- 2Enter the session duration in minutes.
- 3Enter your average heart rate from your watch or app.
- 4Enter your resting and maximum heart rate.
- 5Read your TRIMP and add sessions together for a weekly load.
Formula and method
Banister's training impulse multiplies session duration D (minutes) by the fraction of heart-rate reserve used, HRr, and by a weighting factor y that grows exponentially with HRr. The weighting reflects the way blood lactate rises steeply at higher intensities, so time near maximum counts for far more than time at an easy pace. The constants 0.64/1.92 (men) and 0.86/1.67 (women) come from the lactate response curves used by Banister and colleagues.
HRr is capped between 0 and 1. The session-load labels (light under 50, moderate 50–100, hard 100–200, very hard above 200) are informal guides for a single session, not part of the original method.
- D
- Session duration, minutes
- HRr
- Fraction of heart-rate reserve (0–1)
- HRavg
- Average heart rate for the session
- HRrest
- Resting heart rate
- HRmax
- Maximum heart rate
Worked examples
60-minute run averaging 150 bpm (rest 55, max 190)
Heart-rate reserve is 135 bpm, so 150 bpm is (150 − 55) ÷ 135 = 70.4% of reserve. The male weighting is 0.64 × e^(1.92 × 0.704) = 2.47, and 60 × 0.704 × 2.47 ≈ 104.4 TRIMP.
Woman, 45 minutes at 165 bpm (rest 60, max 185)
165 bpm is 84% of a 125 bpm reserve. The female weighting 0.86 × e^(1.67 × 0.84) = 3.50 gives 45 × 0.84 × 3.50 ≈ 132.2 TRIMP — more than the 60-minute run above in less time.
2-hour easy ride at 135 bpm (rest 50, max 180)
At 65.4% of reserve the load is only about 88 TRIMP per hour, but two hours adds up to roughly 176 TRIMP.
Frequently asked questions
What is a good TRIMP score?+
There is no universal target, because TRIMP depends on your heart-rate reserve and training history. As a rough single-session guide, under 50 is light, 50–100 moderate, 100–200 hard and above 200 very hard. Track your weekly total and change it gradually.
Why does TRIMP use different formulas for men and women?+
Banister's weighting factor was based on how blood lactate rises with heart-rate reserve, and the curves differ on average between men and women. The female constants (0.86 and 1.67) start higher but rise less steeply than the male ones (0.64 and 1.92), so the same heart-rate reserve gives a woman a somewhat higher TRIMP, with the gap narrowing near maximum.
How is TRIMP different from TSS?+
TRIMP is based on heart rate and duration; TSS is normally based on power or pace relative to threshold, scaled so one hour at threshold equals 100. Both measure training load and can feed fitness-fatigue models, but their numbers are on different scales.
Should I use average heart rate for interval sessions?+
Averaging smooths out the hard efforts, which under-counts load because the weighting is exponential. For intervals, calculate each block (warm-up, intervals, recoveries) separately and add the TRIMP values together.
How do I find my resting and maximum heart rate?+
Measure resting heart rate on waking for several mornings and take the lowest typical value. Maximum heart rate is best taken from a hard race or field test; age formulas such as 220 − age can be off by 10–15 bpm.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.