Daily calorie needs:
turn BMR into a number you can eat by

What your daily calorie needs really are

Your daily calorie need is the amount of energy that keeps your weight steady on an ordinary day. It is a moving target, shaped by body size, age, muscle, how much you move and, for some people, medical conditions.

• Body size and composition: a larger, more muscular body needs more energy.
• Age and sex: needs generally fall with age and differ between men and women.
• Movement: walking, standing, housework and training all count.
• Health: pregnancy, breastfeeding, illness and medication can change needs.

No calculator can read that off you directly. What it can do is combine your measurements into an estimate that is good enough to start with, and that you refine using real results.

For most adults, the starting estimate has two parts: the energy you burn at rest (BMR) and an allowance for everything you do on top of that. Together they make up your TDEE.

How to calculate daily calorie needs

1. 1Estimate your BMR from weight, height, age and sex.
2. 2Choose the activity factor that matches an ordinary week, not your best day.
3. 3Multiply the two to get your maintenance calories.
4. 4Add or subtract an amount that fits your goal, as shown in the table below.

The BMR step is covered in detail in the BMR guide, and the choice of multiplier is worked through in the TDEE guide. Here, we start from a BMR you already have.

Worked example: from BMR to a day's calories

This is the energy this person is expected to burn on a typical day. Eating about that amount should hold weight steady; eating less or more moves it down or up.

Sensitivity is worth seeing. With the same BMR, a factor of 1.2 gives 1,980 kcal and a factor of 1.55 gives 2,558 kcal, a spread of about 578 kcal. Honest judgement of your activity matters more than another decimal on the BMR.

Notice that the activity factor already includes exercise. Do not add your workout calories on top, or you will count the same effort twice.

Why the same formula gives very different answers

Two adults of different size and routine can differ by more than 1,000 kcal a day. The table runs three people through the same steps; the factors are examples, not diagnoses of how active anyone really is.

Compare the first two rows. The gap is about 980 kcal a day. Roughly 345 kcal of it comes from body size, age and sex, and the remainder comes from the higher activity factor of a job spent on your feet.

In this table the activity factor explains most of the difference between the first two people, which is why an honest description of an ordinary week matters so much.

This is also why copying a friend's calorie number rarely works. The sensible comparison is between your estimate and your own weight trend.

How your goal changes the number

These adjustments are examples of moderate changes, not prescriptions. Start with the smaller one and see how your weight trend responds over a few weeks.

Whichever way you go, set the target for the next three weeks, not for ever. Your needs shift as your weight, job and routine do, so a number set a year ago is out of date.

A gain target works the same way in reverse. Add a modest amount rather than a large one, which generally adds weight more gradually and with less discomfort.

Spreading your calories across the day

Once you have a number, a simple split makes it usable. Here is one way to divide 2,310 kcal; your own pattern may differ.

If you eat three meals and no snacks, move the snack share into lunch and dinner. If you eat late, keep dinner lighter in the way that suits you. Keep the daily total as the constant and adjust the pattern around it.

A different split is fine. Some people prefer a bigger breakfast, others a bigger dinner, and shift workers eat on a different clock entirely. The total matters more than the exact timing for most people.

Refining the estimate and common mistakes

Treat the estimate as a hypothesis and test it. Eat close to it for two to three weeks and record your weight. If it stays steady, the number works. If you eat an average of 2,450 kcal and your weight is steady, then 2,450 kcal is your real maintenance, whatever the formula said.

A simple way to run the test:

1. 1Eat near your estimate for at least two weeks, logging intake as honestly as you can.
2. 2Weigh yourself under the same conditions on several mornings each week.
3. 3If the weekly average is flat, keep the number. If it rises or falls, adjust intake by 100 to 200 kcal and repeat.

Common errors are worth checking before you change anything:

• Choosing a high activity factor because of one hard workout a week.
• Treating the figure as a fixed number every day. Rest days and busy days differ.
• Never updating the number after weight, job or training changes.
• Using adult estimates for children, teenagers, pregnancy or breastfeeding, where needs differ.
• Eating back exercise calories shown by a watch on top of an activity factor.

If you manage a condition such as diabetes or thyroid disease, or want to change your weight by a large amount, ask a doctor or registered dietitian to set your targets.