Calorie and TDEE Calculator

What the calculator works out

Two numbers, in order. First your basal metabolic rate, the energy your body spends staying alive with no activity at all. Then your total daily energy expenditure, which is that figure multiplied by how much you move.

BMR runs 60 to 70 percent of daily energy use for most adults, which surprises people who assume exercise dominates. A 30-year-old man at 175 cm and 70 kg burns about 1,650 kcal doing nothing. Training moderately five days a week takes his total to roughly 2,550.

BMR versus TDEE pulls the two apart properly, including the three components that sit between them: the energy cost of digesting food, deliberate exercise, and the fidgeting and pacing that varies by hundreds of calories between people.

What TDEE means

TDEE stands for total daily energy expenditure. It is every calorie you burn in 24 hours, added up. Eat that many and your weight holds. Eat fewer and you lose, eat more and you gain, and almost every diet plan you have ever read is a rule for picking a number on one side of it.

Four things make up the total:

• Basal metabolic rate, 60 to 70 percent. Breathing, circulation, temperature, tissue repair. It scales with body size, which is why a heavier person burns more at rest.
• The thermic effect of food, around 10 percent of what you eat. Digestion costs energy. Protein costs the most, which is a small part of why high-protein diets are easier to lose weight on.
• Exercise, anywhere from 0 to 30 percent depending entirely on you.
• Everything else you do while awake. Walking to the car, standing, cooking, tapping a foot. This is the component that varies most between two people of the same size, and it is also the one that quietly falls when you start dieting.

The calculator estimates the first from your body and bundles the other three into the activity multiplier. That bundling is where the error lives, which is the next problem.

The Mifflin-St Jeor equation

This calculator uses Mifflin-St Jeor, published in 1990 and now the default in most clinical settings:

• Men: BMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age) + 5
• Women: BMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age) – 161

It replaced the 1919 Harris-Benedict equation because it predicts measured resting expenditure more closely across a wider range of body sizes. Harris-Benedict was built on a sample of young, lean, mostly male subjects and overestimates by 5 percent or so for people who look nothing like them.

Both equations take weight rather than lean mass, so both overestimate for someone carrying a lot of fat and underestimate for someone very muscular. The Katch-McArdle equation uses lean mass instead and beats both, if you know your body fat percentage. The body fat calculator will give you that figure from a tape measure.

Activity multipliers

This is where most of the error creeps in. The gap between 1.2 and 1.9 is about 1,150 kcal a day for the same body, and people overrate themselves by a full step routinely. Four gym sessions a week on top of a desk job is light to moderate, not active. Picking the right activity multiplier gives concrete descriptions for each band.

Maintenance calories by weight

Maintenance calories and TDEE are the same number under two names. These tables run the equation above at a fixed height and age so you can see roughly where you land before you type anything in. Men are calculated at 5 ft 10 in and women at 5 ft 5 in, both at age 35. Ten years older takes 60 to 85 kcal off these figures and every extra inch of height adds 20 to 27, depending which activity column you are reading.

Look down a column rather than across a row and you can see why weight loss slows. A 190 lb sedentary man maintains on 2,170. At 170 lb he maintains on 2,060. He has lost 20 lb and his body now needs 110 fewer calories a day, so the deficit he started with has shrunk by that much without him changing anything.

Look across a row instead and the activity column matters more than most people expect. The same 150 lb woman maintains on 1,650 sitting still and 2,370 training hard. Guessing that column wrong costs you 720 calories of accuracy, which is more than most people’s entire intended deficit.

Calories for losing, holding and gaining

The three figures under the result apply a 500 kcal offset either side of your TDEE. A pound of body fat stores roughly 3,500 kcal, so 500 a day for a week is the classic one-pound target.

The arithmetic holds early and loosens later. A lighter body burns less, so the deficit that produced a pound a week in month one produces less by month four unless you recalculate. Adaptive thermogenesis takes another slice: energy expenditure falls slightly beyond what the weight loss alone predicts.

How big your calorie deficit should be covers why an aggressive cut costs you muscle and why 0.5 to 1 percent of body weight per week is the range worth aiming at.

How many calories to eat a day to lose weight

Take your maintenance figure and subtract 500. That is the whole method, and worked through at moderate activity it looks like this:

Two adjustments to that flat 500. If you are heavier, you can afford more: a percentage of body weight scales better than a fixed number, and 0.5 to 1 percent a week is the usual range. A 230 lb man losing 1 percent is dropping 2.3 lb a week, which needs a deficit near 1,150. A 130 lb woman at the cautious end of the same range is chasing 0.65 lb a week, which needs about 325, so the flat 500 already puts her at the top of the range rather than the middle of it.

The other adjustment is patience. Bigger deficits do not reliably produce faster fat loss, because more of what comes off is muscle and adherence collapses somewhere around week three. The deficit you actually hold for four months beats the one you abandon in week two.

Is 1,200 calories a day enough?

1,200 for women and 1,500 for men are the floors most clinicians use for unsupervised dieting. Below them it gets hard to hit protein, calcium, iron and B vitamins from food, and the risk stops being theoretical.

For most people 1,200 is not a target, it is a symptom of a bad plan. Look at the women’s table: a sedentary 130 lb woman maintains on 1,540, so 1,200 is a deficit of only 340 and produces about two thirds of a pound a week. A moderately active woman at the same weight maintains on 1,990 and would be cutting nearly 800, which is more than she should.

Eating below your floor is a signal to move more rather than eat less. Adding a daily walk moves a sedentary 130 lb woman from 1,540 to about 1,770, and a 500 kcal deficit off that lands at 1,270 with a full pound a week still on the table. If you have a medical reason to eat under those floors, that belongs with a doctor rather than a calculator.

Treat the output as a starting point

Any prediction equation carries error of roughly 10 percent in either direction, and self-reported activity adds more. The number on the screen is a hypothesis. Eat at it for two weeks, weigh yourself under consistent conditions, and adjust based on what your own body did.

Use weekly averages, not single readings. Day-to-day weight moves on water and gut contents by more than a week of careful eating moves fat, which is the fastest way to talk yourself out of a plan that is working. Why the scale jumps overnight explains what is actually moving.