Fitness calculators

Your basal metabolic rate (BMR) uses the Mifflin-St Jeor equation, the formula the British Dietetic Association and most clinicians use:

BMR = (10 x weight kg) + (6.25 x height cm) − (5 x age) + s
s = +5 for men, −161 for women

Your TDEE (total daily energy expenditure, the calories you burn in a day) is BMR multiplied by an activity factor of 1.2 to 1.9. Weight-change targets assume roughly 7,700 kcal per kg of body mass and cap the rate at a safe 0.5 to 1.0 kg per week.

Informational only, not medical or dietary advice. Editorially reviewed by FitCalcs, with each figure citing its source.

BMI = weight (kg) divided by height (m) squared. NHS categories: under 18.5 underweight, 18.5 to 24.9 healthy, 25 to 29.9 overweight, 30 and over obese.

BMI = weight ÷ (height_m × height_m)

Waist-to-height ratio = waist ÷ height (same units). The NHS now treats 0.5 or above as a sign of increased health risk regardless of BMI, because it reflects central fat. It is a better single number than BMI for many people.

Informational only, not a medical diagnosis. BMI does not distinguish muscle from fat. Editorially reviewed by FitCalcs, with each figure citing its source.

Predictions use Riegel's endurance formula, the model running coaches and race calculators have used since 1981:

T2 = T1 × (D2 ÷ D1)^1.06

T1 is your known time over distance D1; the 1.06 exponent reflects how pace slows as distance grows. It assumes equivalent training and even pacing, so longer races (especially the marathon) are best-case estimates, not guarantees.

For information only. Build distance gradually and train for the event you are targeting.