How calorie targets are calculated

Step 1: resting energy

Your body uses energy even at rest — to breathe, circulate blood and keep warm. This is your basal metabolic rate (BMR). It can’t easily be measured outside a lab, so it’s estimated with an equation.

We use the Mifflin–St Jeor equation, published in 1990, which estimates BMR from weight, height, age and sex. It’s widely used because it performs well across a broad range of adults.

Step 2: everyday activity

BMR is multiplied by an activity factor to estimate total daily energy expenditure (TDEE): roughly 1.2 if you mostly sit, up to about 1.9 for very physical jobs or twice-daily training.

This is the biggest source of error. People often overestimate how active they are, so if you’re unsure, pick the lower option and adjust later.

Step 3: your goal

To maintain weight, your target is your TDEE. To gain, we add 250–500 kcal a day.

To lose weight we subtract around 275 kcal a day for a gentle pace or 550 kcal for a steady pace — roughly 0.25 kg or 0.5 kg a week, using the common rule of thumb that about 7,700 kcal corresponds to 1 kg of body weight. That rule is an approximation: weight loss tends to slow over time as your body adapts, which is one reason to review your target every few weeks.

The NHS recommends losing weight gradually, at a rate you can keep up.

The limits we never cross

Whatever the maths says, these rules always apply:

• Targets never go below 1,200 kcal a day for women or 1,500 kcal for men. Very low calorie diets should only be followed with medical supervision.
• The deficit is never more than 25% of your maintenance energy.
• No weight-loss target for under-18s, who are still growing.
• No deficit during pregnancy or breastfeeding.
• No deficit if your BMI is already below the healthy range.
• If you tell us you have a history of disordered eating, we switch to calm mode and keep numbers in the background.

Using your target well

Treat the number as a starting point. Track your weight trend over two to four weeks, not day to day — weight naturally moves by a kilogram or more because of water, salt and food in transit.

If you’re consistently above or below your target and your weight isn’t doing what you expect, adjust by 100–200 kcal and review again. And if you have a medical condition, your GP or a registered dietitian should guide your targets.