Time gain per mile
-- s/mi
Weight Loss Performance Gain
This calculator estimates the impact of moderate weight loss (mainly reliable up to 5% of body
weight)
on your running speed and time per kilometer.
For the calculation to be correct, it must be excess weight compared to race weight.
Enter your weight and reference pace
Metric
Imperial
Estimated results
Weight lost
--
Relative loss
-- of body weight
Estimated new pace
--:-- min/mi
Gain on a 10K race
--
Frequently Asked Questions
How much time do you save by losing 1 kg?
On average, losing 1 kg of excess weight gives you approximately 1.4% more speed for a 70 kg runner. That represents about 3 minutes on a marathon at a 5:00/km pace, or roughly 13 seconds per km.
Is the 1% speed per 1% weight loss rule reliable?
This approximation from physiological research is mainly reliable for moderate losses, up to about 5% of body weight. Beyond that, factors like muscle loss, fatigue, and energy deficit can reduce or even negate the gains.
How much time do you save on a 10K by losing 3 kg?
For a 70 kg runner at 5:00/km, a 3 kg loss (4.3% body weight) saves approximately 2 min 09 s on a 10K, going from 50:00 to about 47:51.
What is the impact of weight loss on a marathon?
The impact is proportional to the distance. For a 70 kg runner at 5:00/km:
- −3 kg → gain of about 9 min on the marathon
- −5 kg → gain of about 15 min
- −1 kg → gain of about 3 min
Does this formula apply to trail running and hills?
Weight has an even greater impact on uphills: the extra energy cost per kg is amplified by the gradient. In trail and mountain running, the effect of weight loss on performance is more pronounced than on flat roads.
Details on the model used
This approximation comes from physiological analyses: in running, carrying less mass costs slightly less energy, which allows running slightly faster at equal intensity.
- The 1% weight lost ≈ 1% speed gained relationship is mainly valid for modest losses (up to ~5%).
- To optimize your weight loss, use our calories burned calculator to track your energy expenditure
- Once your new pace is calculated, you can estimate your new times on different distances
- Also adapt your training zones according to your new weight
- Don't forget to calculate your speeds and paces for your daily runs
- Check your BMI to assess your body composition
- Learn how running helps with weight loss over time
- Beyond that, other factors come into play (strength loss, fatigue, lack of energy).
- This calculation doesn't replace medical or nutritional monitoring.
Use this tool as an order of magnitude to visualize the effect of reasonable weight loss, alongside regular and progressive training.