How many calories do you need? A simple guide

Calories measure the energy in food and drink, and the energy your body uses. If you eat about the same as you use, your weight tends to stay steady. The NHS explains that consuming less energy than your body uses leads to weight loss, because your body draws on stored fat for energy.

The averages

The NHS gives guideline daily amounts of about 2,500 kcal for men and 2,000 kcal for women. It stresses that your own needs vary with your age, weight, height and how much exercise you do. So averages are a starting point, but you can do better with a few numbers about yourself.

Step 1: your resting energy (BMR)

Your body burns energy even if you stay in bed all day, to keep your heart beating, your lungs breathing and your temperature steady. This is your basal metabolic rate, or BMR.

A widely used way to estimate it is the Mifflin-St Jeor equation, published in 1990. It was developed from measurements of resting energy expenditure in 498 healthy adults aged 19 to 78. The simplified versions are:

• Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
• Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161

The original study found that the older Harris-Benedict equations from 1919 overestimated measured resting energy by 5%.

Step 2: add your activity

Multiply your BMR by an activity factor to get your “maintenance” calories, which are the calories you burn in a typical day:

These multipliers are common rules of thumb, not exact measurements. Most people overestimate how active they are, so if you are unsure, choose the lower one.

A worked example

A 30-year-old woman, 165 cm tall, weighing 65 kg, who exercises about twice a week:

1. BMR = 10 × 65 + 6.25 × 165 − 5 × 30 − 161 = about 1,370 kcal
2. Maintenance = 1,370 × 1.375 = about 1,880 kcal

That is close to, but not the same as, the NHS average of 2,000 kcal for women. Your numbers will differ from the averages too.

Step 3: adjust for your goal

• To stay the same: eat around your maintenance.
• To lose weight: eat somewhat less. The NHS suggests losing weight steadily, at 0.5 to 1 kg a week. Read the healthy pace of weight loss.
• To build muscle: a small surplus may help, but training matters more than eating a lot extra.

The NHS notes that very low calorie diets, under 800 or 1,200 calories a day, are not suitable or safe for everyone, and says support may come from a GP or dietitian. That is why our calculator will not go lower than 1,200 kcal for women or 1,500 kcal for men. That limit is our own cautious choice, not an official rule.

Why two calculators give different answers

Calculators use different equations, different activity multipliers and different rounding, so they can disagree by a few hundred calories. Neither is the “truth”. They are estimates of an average person like you. What happens when you follow the number for a few weeks is far more useful information than the number itself.

Calories and training

When you start strength training, your needs rise a little because you move more, but not as much as many people think. The activity multiplier already includes your exercise, so do not add the calories shown on a gym machine or a watch on top. If you feel low on energy in your workouts, check that you are eating enough and sleeping well.

Use your number as a starting point

Estimates are not exact, so treat them as an experiment:

1. Follow the number for 2–3 weeks.
2. Weigh yourself once a week, at the same time of day, and watch your energy levels and how your clothes fit.
3. If nothing changes after 2–3 weeks and you want it to, adjust by about 100 kcal a day.

You do not need to count calories forever. Many people use it for a few weeks to learn what portions look like.

If you do not want to count

Counting is optional. Many people use these simple habits instead:

• Eat regular meals built around vegetables, fruit, protein and whole grains.
• Pay attention to portion sizes and to hunger and fullness.
• Drink mostly water, and keep sugary drinks occasional.
• Weigh yourself or check how your clothes fit about once a week.

If your weight is not moving in the direction you want after a few weeks, make a small change.

Who should not use a calorie estimate

Please do not use this approach if you are under 18, pregnant or breastfeeding, have a medical condition that affects your diet, or have or have had an eating disorder. Counting can be stressful for some people. If so, talk to a doctor or registered dietitian instead.

Frequently asked questions

Is the NHS average of 2,000 and 2,500 calories right for me?

It is an average. The NHS stresses that your own needs vary with age, weight, height and how much exercise you do. Use the calculator for a more personal estimate.

Do I eat back the calories I burn in the gym?

No. The activity level you choose already includes your exercise.

Why does the equation need my sex?

The Mifflin-St Jeor equation has two versions because average resting energy differs between men and women. We use the version that you choose.

Can I just trust the number?

Treat it as a starting point and adjust based on real life. Our calculator gives you a gentle target.