Everything you need to know about the calories you burn

Your body burns about 1.2 to 1.9 times its resting burn every day. The US Dietary Guidelines’ tables put most adults between 1,600 and 3,000 calories. A calculator gets you within a few hundred, and four weeks of food logs and morning weigh-ins tell you the rest.

Why does every calculator give you a different number?

Type the same height, weight and age into three calculators and you can get three answers hundreds of calories apart. Your watch gives you a fourth. Pick the one you like, eat to it for two weeks, and when the scale doesn’t move it’s easy to decide calories don’t work for you.

Every one of those numbers is a forecast. A weather forecast is usually close and sometimes wrong, and the rain gauge in your yard says what actually fell. A calculator is the forecast. Your scale, over a few weeks, is the rain gauge.

The forecasts disagree for two reasons. Each calculator starts from a formula for your resting burn, and the best of them, Mifflin-St Jeor, came within 10% of a lab measurement for 82% of 337 adults in a 2013 test. That leaves about one person in five more than 10% off. Then each calculator multiplies by an activity level you picked from a word like “moderately active”, and that word moves the answer by hundreds of calories. Your step count can pick it for you.

The whole thing in one picture

Think of your calories as a household budget. Your resting burn is the rent. It’s big, it’s due every day, and you pay it whether you go out or not. Your heart, brain, liver and kidneys never stop, and unlike a car engine, your body never switches off. Exercise is dinner out: memorable, under your control, and small next to the rent.

Sleep shows it best. A 155 pound person burns about 630 calories in nine hours of sleep and about 110 running a mile at 6 miles an hour, going by the 2024 Compendium of Physical Activities. A night in bed costs more than five times what the run does.

The rest of the day’s spending splits three ways. Digesting food costs about 10% of what you eat. Everyday movement, from walking to the car to standing at the stove, is the part that varies most between people. Workouts are often the smallest slice.

The eight parts of the guide

1. Where your calories go. Resting burn, daily movement, exercise and digesting food, sized for a real person.
2. The formulas, and why calculators disagree. Four formulas from 1918 to 1991, how far off each can be, and which to use.
3. Your activity level, from your steps. Why going to the gym three times a week doesn’t make you moderately active.
4. How many calories to eat to lose weight. The pace, the floor, and your protein.
5. Why you’re not losing weight in a deficit. Every gap between the plan and the scale, sized in calories.
6. Is your watch’s calorie number right? What it measures well, what it guesses, and how to use it.
7. Does metabolism slow with age? Flat from 20 to 60, then a slow fall. What changes before that is muscle and movement.
8. Measure your real TDEE in four weeks. The arithmetic, the traps, and how often to redo it.

The numbers in one table

Three things most people get wrong

They think their metabolism broke in their 30s. In a 2021 study of 6,421 people aged 8 days to 95 years, the calories burned each day, adjusted for body size, held steady from 20 to 60. The section on metabolism and age has the curve.

They trust the watch. In a Stanford test of seven wrist devices on 60 people, no device got calories burned within 20%, and the worst missed by 93%. Most of the same devices got heart rate within 5% on a bike. Your watch’s calorie number covers how to use it anyway.

They pick “moderately active” for three gym sessions. For a 200 pound man who walks 4,000 steps a day and lifts three hours a week, that word adds about 540 calories a day he doesn’t burn. Your activity level shows the arithmetic.

Tracking it

In Gyroscope you photograph your meals, weigh in most mornings and let your steps come in from your phone or watch. A Withings or Apple Health scale syncs on its own, or you can photograph any scale’s display. Your meals and weigh-ins feed your energy balance, your weight trend gives a calorie-burn estimate, and your TDEE gets its own trend. That’s the four-week measurement in measure your real TDEE, running every week. More on tracking it.