Health and Fitness Calculators

What Can Health Calculators Tell You About Your Weight and Calories?

Health calculators can give you a sensible estimate of whether your weight is in a healthy range and how many calories your body uses each day, but they cannot diagnose anything. They turn your height, weight, age, sex and activity level into a starting point you can discuss with your GP or a dietitian.

Begin with the BMI Calculator, which divides your weight in kilograms by your height in metres squared. For most adults a BMI of 18.5 to 24.9 is the healthy range, but NICE guidance uses a lower threshold of 23 for overweight in people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African Caribbean family background, because health risks rise at a lower BMI. BMI also cannot tell muscle from fat, so a waist measurement under half your height is a useful second check.

For calories, the TDEE Calculator starts from your basal metabolic rate and multiplies it by an activity factor. Be honest about activity, as choosing very active when you have a desk job is the most common reason results come out too high. Formulas such as Mifflin-St Jeor are good averages but can be about 10% out for an individual. The BMR Calculator compares three formulas side by side, which shows how much estimates can vary for the same person.

Weigh yourself at the same time of day on the same scales, and track the trend over two to four weeks rather than reacting to daily changes caused by water and salt. Health calculators are not designed for use during pregnancy, for children, or for anyone with an eating disorder, where a GP or midwife should guide you. Treat health calculators as general information only. If your weight changes quickly without trying, speak to your GP rather than relying on any calculator.