Free health calculators

What are our health calculators for?

Our calculators turn a few simple measurements into information you can use. They answer everyday questions such as “Is my waist size a health risk?”, “How many calories does my body need?” or “How much did that walk really do?”.

We built them because many online tools feel cold, stop working above a certain weight or push extreme diets. Ours are different in three ways.

First, every tool is free and works for larger bodies. Second, the results come with honest context, including when a number is less reliable. Third, the advice that follows is always about good food, appropriate exercise and walking, at a level that fits you today.

None of the calculators diagnoses a condition. The Lancet Commission on clinical obesity stressed that health should be judged by how the body and daily life are affected, not by a single figure. Think of the results as a helpful starting point.

Body and weight calculators

These six tools describe your body size and shape, and help you follow change over time. If you only try two, start with BMI and waist-to-height ratio.

• BMI calculatorYour body mass index, category, healthy range and BMI Prime.
• Healthy weight calculatorThe weight range that fits your height, in kg or lb.
• Waist-to-height ratio calculatorChecks belly fat, with an optional waist-to-hip ratio.
• Body fat calculatorEstimates body fat percentage with a tape measure.
• Weight loss calculatorEstimates when you could reach a goal at a steady pace.
• Weight loss percentage calculatorShows how much you have lost and your 5, 10 and 15% milestones.

Food and energy calculators

These four tools help you plan meals and drinks. They estimate what your body needs, so you can make changes without guessing or going too low.

• Calorie calculatorThe calories your body uses at rest and in a normal day.
• Calorie deficit calculatorA daily calorie target for gentle, safe weight loss.
• Macro calculatorRanges for carbohydrate, fat, protein and fibre.
• Water intake calculatorHow much to drink each day, adjusted for exercise and heat.

The calorie deficit calculator never suggests less than 1,200 kcal a day for women or 1,500 kcal for men. Eating less than that without medical supervision makes it hard to get enough nutrients and is rarely sustainable.

Movement calculators

These two tools show what your activity is worth and how hard to work. They are especially useful if you are starting with walking or our Start workouts.

• Calories burned calculatorEnergy used by walking, swimming, dancing, housework and more.
• Heart rate zones calculatorLight, moderate and vigorous heart rate ranges for your age.

Pregnancy calculator

Pregnancy is not a time for dieting. This tool shows the healthy amount of weight to gain, based on your weight before you became pregnant.

• Pregnancy weight gain calculatorRecommended total and weekly gain for one baby.

Always follow the advice of your midwife or doctor. Our page on obesity and pregnancy explains what extra care you can expect.

Which calculator answers which question?

Each calculator answers one clear question, and each has limits you should know about. The table puts all thirteen side by side.

The formulas behind the tools come from large studies. The waist-to-height ratio, for example, was better than BMI or waist size alone at spotting risks such as diabetes and high blood pressure in a review of 31 studies with more than 300,000 adults.

For daily calories we use the Mifflin-St Jeor equation. An expert review found it the most reliable of the common formulas: it came within 10% of measured resting energy use in more people than the others. Errors of more than 10% still happen in some people.

Maximum heart rate is estimated as 208 minus 0.7 times your age. That formula comes from 351 studies with 18,712 healthy adults, and your own maximum can be higher or lower.

Weight loss tools also need care. Researchers showed that the old rule of 3,500 kcal for every pound lost clearly overestimates weight loss over time, because the body adapts. Treat every goal date as a rough guide.

How do you get reliable results?

A calculator is only as good as the numbers you give it. A few habits make your results much more useful.

• Measure the same way each time. Same scale, same tape, same time of day, ideally in the morning before breakfast.
• Use your height without shoes. If you have not been measured for years, ask someone to help, or measure against a wall.
• Look at trends, not single readings. Weight goes up and down from day to day with fluid and food. A monthly check shows the real direction.
• Read the guide under each tool. It explains the formula, who should be careful and how to read your result.

Using numbers kindly

Numbers about our bodies can bring up strong feelings. Many people living with obesity have heard their BMI read out in a way that felt like blame. That should never happen, and it will not happen here.

A result is a guide, not a judgement. It does not measure your effort, your character or your value. Weight is shaped by genes, sleep, stress, medicines, income and the food around you, as our page on the causes of obesity shows.

It helps to aim for change you can feel, not just a number. In a large study of adults with type 2 diabetes, losing 5 to 10 per cent of body weight already improved blood sugar, blood pressure and blood fats for many people. Better fitness, sleep and mood count just as much.

Your waist can also shrink with regular movement even when the scale stays still, an expert consensus has noted. That is real progress.

If numbers about your body tend to trigger restriction, bingeing or distress, or you have a history of an eating disorder, it is fine to skip these tools. Please talk to your doctor or care team, who can follow what is needed in a safe way.

If you are pregnant, have diabetes, or take medicines for blood pressure or blood sugar, check with your doctor before changing how you eat or move.

Is anything you enter stored?

All calculations happen on your own phone, tablet or computer. When you press Calculate, the sum runs in your browser and the answer appears on your screen.

Your weight, height, age and other details are not sent to Obesity Foundation, not saved in a database and not shared with anyone. Close the page and they are gone.

If you would like to keep track of your progress, you can choose to do so in the free Obesity Foundation Club, where you decide what to log.

Where can you get free help after your result?

A number is only useful if it leads to a step you can take. Obesity Foundation is a non-profit, and everything we offer is free.

• A free eating plan with everyday meals and no crash diets. Request your eating plan, or read more about our eating plan first.
• Free workout videos in three levels, starting with gentle seated sessions. Get the free videos or browse our workouts.
• A walking plan that starts at five minutes a day. See our guide to walking for weight loss.
• A free video meeting (in English) with our team to talk about your results and next steps. Book a video meeting.
• The Obesity Foundation Club, a free private account to log walks, workouts and progress. Join the club.

Looking for a doctor, dietitian or local group? Our find help page shows where to start.