Check your BMI, calorie needs, body fat and more with simple calculators that use metric units first.
Our health and fitness calculators help you understand your body and plan your training. Estimate body mass index, daily calories, protein, water intake, heart rate zones and one rep max, or track sleep, pace and pregnancy dates. Each tool explains what the number means in plain language.
How do I calculate my BMI?
To calculate your BMI, divide your weight in kilograms by your height in meters squared. A result from 18.5 to 24.9 is classed as a healthy weight for most adults. Our health calculators do the maths for you in metric or imperial units and explain what your result means.
Height is entered in centimeters and weight in kilograms by default, which matches how most people in the UK, Ireland and the EU measure themselves, with stones, pounds and feet and inches available where useful. These calculators give general estimates only and do not replace advice from a doctor, midwife or registered dietitian.
Weight and Body Composition
BMI, body fat, ideal weight and waist ratios
Calories and Nutrition
Energy needs, deficits, macros, protein and water
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What Do Health Calculators Actually Measure?
Health calculators turn a few measurements into an estimate, such as body mass index from height and weight or daily energy needs from age, size and activity. They are screening and planning aids, not diagnoses, and each one answers a narrow question. Knowing that question helps you read the result sensibly.
The BMI calculator compares weight with height, the body fat calculator estimates the share of your weight that is fat from tape measurements, and the calorie calculator estimates how much energy you use in a day. Used together, these health calculators give a fuller picture than any single number, because each covers a weakness in the others.
Treat every result as a starting point for a conversation with a GP, pharmacist or dietitian, especially if you are pregnant, under 18, an athlete or managing a long term condition.
Measure consistently for the most useful results. Weigh yourself at the same time of day, ideally in the morning before eating, and measure your waist midway between the bottom of your ribs and the top of your hips. Small changes in method can move a result more than a week of real progress.
What Is a Healthy BMI for Adults in the UK?
The NHS classes a BMI of 18.5 to 24.9 as a healthy weight for most adults, 25 to 29.9 as overweight and 30 or more as obese. BMI is weight in kilograms divided by height in meters squared, so a person who weighs 70 kg and is 1.75 m tall has a BMI of 22.9.
The NHS uses lower thresholds for people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African Caribbean backgrounds, because health risks tend to rise at a lower BMI. For these groups, 23 to 27.4 counts as overweight and 27.5 or higher as obese.
BMI cannot tell muscle from fat, so a muscular person may score as overweight while being lean. That is why the NHS also suggests keeping your waist to less than half your height. A waist to height ratio below 0.5 is a simple check that reflects fat stored around the middle, which is linked to higher risk of type 2 diabetes and heart disease.
BMI ranges in this guide apply to adults. Children and teenagers are assessed with age and sex specific centile charts, so an adult BMI result should not be used to judge whether a young person is a healthy weight.
How Many Calories Do You Need Each Day?
NHS guidance says an average man needs about 2,500 kcal a day and an average woman about 2,000 kcal, though your own figure depends on age, size and how active you are. Those averages are a reference point, not a target, which is why a personal estimate is more useful.
Calorie tools usually start with basal metabolic rate, the energy your body burns at rest. The widely used Mifflin St Jeor equation gives 10 × weight in kg + 6.25 × height in cm − 5 × age, plus 5 for men or minus 161 for women. That figure is then multiplied by an activity factor, from about 1.2 for desk based days to about 1.9 for very hard physical work.
For gradual weight loss, many people aim for a modest daily deficit rather than a severe cut, and slow, steady change is easier to keep up. Check your estimate every few weeks against real progress, since energy needs fall slightly as weight drops.
Protein, water and activity matter too. A balanced plan spreads energy across meals, includes regular movement and leaves room for rest days, which makes the numbers easier to stick to over months rather than weeks.
| Measure | What it estimates | Reference value | Source |
|---|---|---|---|
| BMI | Weight relative to height | Healthy 18.5 to 24.9; overweight 25 to 29.9; obese 30 or more | NHS |
| BMI (adjusted groups) | Same, for higher risk ethnic groups | Overweight 23 to 27.4; obese 27.5 or more | NHS |
| Waist to height ratio | Fat stored around the middle | Keep waist to less than half your height (below 0.5) | NHS |
| Daily calories | Average energy needed per day | About 2,500 kcal for men, 2,000 kcal for women | NHS |
| BMR (Mifflin St Jeor) | Energy burned at complete rest | 10W + 6.25H − 5A + 5 (men) or − 161 (women) | Mifflin et al., 1990 |
Frequently Asked Questions
Are health calculators accurate?
They are accurate estimates for the average adult, not diagnoses. Formulas such as BMI cannot account for muscle mass, age or ethnicity, so use results as a starting point and discuss concerns with a healthcare professional.
Can I enter height in centimeters and weight in kilograms?
Yes. Metric units are the default on every health calculator, and you can switch to feet, inches, stones or pounds with one click. Results are converted automatically, so you can compare both systems without extra maths.
What is a healthy BMI range?
For most adults, the World Health Organization and the NHS define a healthy BMI as 18.5 to 24.9. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or more is obese, though ranges can differ for some groups.
Do these calculators replace medical advice?
No. They provide general estimates for education and planning. Always speak to a doctor, midwife, pharmacist or registered dietitian before changing your diet, starting intense exercise or making decisions about pregnancy or medical conditions.
Is any health information saved?
No. Calculations happen in your browser and your age, weight and other details are not stored in an account or shared with third parties. Refreshing the page clears everything you entered.
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Last reviewed: October 2026