How to use the calorie calculator
- Age and sex, in years, and male or female. Both feed straight into the formula.
- Height and weight. The Units dropdown swaps between metric (cm, kg) and imperial (ft, in, lb), and the fields change with it, so you never have to convert anything by hand before typing.
- Activity level, from sedentary up to extra active.
- Goal, maintain, lose or gain. Lose and gain shift your target by 500 calories a day.
- Read the first row: maintenance calories, goal calories, BMR.
- Below it sits a protein, carbs and fat row, which turns your goal calories into a rough gram target for each of the three.
- At the bottom, the calories by goal panel puts lose, maintain and gain side by side.
How your daily calories are worked out
The starting point is your BMR, or basal metabolic rate. That is the energy you burn lying still and doing nothing. This tool uses the Mifflin-St Jeor equation. For men it is10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5. For women it is10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161. Mark Mifflin, Sachiko St Jeor and their co-authors published it in the American Journal of Clinical Nutrition in February 1990. A 2005 review in the Journal of the American Dietetic Association tested it against Harris-Benedict and two others. It came within 10 percent of measured resting rates more often than any of them, in obese and non-obese adults alike. That is why most dietitians reach for it first.
Your BMR is then multiplied by an activity factor. That gives yourTDEE, or total daily energy use, which the tool labels maintenance calories. The five factors are Sedentary 1.2, Lightly active 1.375 for one to three days of exercise a week, Moderately active 1.55 for three to five days, Very active 1.725 for six or seven days, and Extra active 1.9 for very hard training or a physical job. Moderately active is the default.
Your goal then shifts that figure. Maintain leaves it alone, Lose takes off 500 a day, Gain adds 500.
The macro row splits your goal calories, not your maintenance calories. It uses 30 percent protein, 40 percent carbs and 30 percent fat, at 4 calories per gram for protein and carbs and 9 for fat. Pick Lose weight and all three gram figures drop with the target. The calories by goal panel works the other way round on purpose. It is always built from maintenance, so those three numbers stay put whatever goal you choose above. You get the deficit, the maintenance line and the surplus in one view, with no clicking back and forth.
Switch to imperial and heights convert at 2.54 cm per inch, weights at 2.20462 lb per kg. The same body gives the same answer either way.
Why 500 a day stops being a pound a week
That 500 figure is not arbitrary. It traces back to a 1958 paper by Max Wishnofsky in the American Journal of Clinical Nutrition. He put the energy in a pound of body fat at roughly 3,500 calories. Seven days at minus 500 makes 3,500, so a pound a week. The sums are fine. The biology is not, because the rule is static. It quietly assumes a lighter body burns as much as the heavier one it replaced.
Kevin Hall's team at the National Institute of Diabetes and Digestive and Kidney Diseases built theNIH Body Weight Planner around a model that does track the drop. NIDDK says plainly that you "lose much less weight in reality" than the old rule promises. The gap is wide. Take a 35 year old man of 200 lb who cuts 500 calories a day and holds it. The 3,500 rule says he hits a 23 lb loss in about four months. The NIH model says the same 23 lb takes him roughly a year. Carson Chow, one of the modellers, offers a blunter rule of thumb. Every 10 calories a day you drop for good is worth about a pound in the end, with half of it inside the first year and the rest taking around three.
So read your goal number as an instruction for this week, not a forecast for next summer. Weigh yourself a few times a week and take the average. If that average has not moved in a fortnight, take off another 100 or 150 and watch again. That beats trusting any one calculation, this one included. You can read the model itself on theNIH Body Weight Plannerpage.
Everything here runs in your browser as you type. The age, height and weight you enter feed the sums on screen and are not sent anywhere.
An estimate, not a diagnosis
Medical disclaimer: This calculator is general information, and it is not medical advice. Your calorie needs move with genes, hormones, muscle mass, medication and health conditions, none of which a height-and-weight formula can see, so treat the result as a starting point and adjust it on real progress rather than on the first number you are given. Talk to a doctor or a dietitian before you make big changes to your diet. That goes double if you are pregnant, breastfeeding, under 18, or living with diabetes or an eating disorder. When in doubt, ask.
Frequently asked questions
How many calories should I eat a day?
It depends on your age, sex, height, weight and how much you move. The tool works out your maintenance level with Mifflin-St Jeor, then applies your goal. Plenty of adults land between 1,800 and 2,800 a day. Tall, heavy or very active people sit well above that, and small, quiet-living people sit below it.
How is BMR calculated here?
With the Mifflin-St Jeor equation. Men: 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5. Women: 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161. The answer is the energy your body uses at complete rest.
What is TDEE, and how is it different from BMR?
BMR is resting energy on its own. TDEE is that BMR times an activity factor between 1.2 and 1.9, so it covers walking, work, training and the rest of a normal day. The tool shows TDEE as your maintenance calories. Eat at that level and your weight should hold roughly steady.
Does cutting 500 calories a day really lose a pound a week?
Early on, near enough. Later, no. The pound a week claim rests on Wishnofsky's 1958 figure of 3,500 calories per pound of fat. It ignores the way a lighter body burns less. Expect the loss to slow month by month, and to flatten out if the deficit stays the same size.
Are the macro grams based on my goal calories or my maintenance calories?
Your goal calories. The split is 30 percent protein, 40 percent carbs and 30 percent fat, so choosing Lose weight pulls all three gram figures down with the target.
Is this calorie calculator accurate enough to rely on?
It is a good first estimate, not a measurement. Mifflin-St Jeor was built on population averages. Two people of the same height and weight can differ by several hundred calories at rest. Use the number for a fortnight, look at what the scales did, then adjust.