TDEE and Calorie Deficit Calculator UK: How Many Calories to Lose Weight

Your total daily energy expenditure (TDEE) is the number of calories that keeps your weight steady. The calculator above works it out from your age, height, weight and how active you are, then shows what to eat to lose weight and how long that is likely to take. This guide explains where each number comes from, how big a deficit the NHS suggests, and why weight loss slows down over time.

What Is TDEE?

TDEE is the total calories you use in a day: your resting calories (BMR) plus everything you do.

TDEE is the total number of calories your body uses in a day. It has two main parts:

• Basal metabolic rate (BMR): the energy your body uses at complete rest, to keep your heart, lungs and brain working. For most people this is the larger part.

• Everything else: walking, working, exercise, everyday movement and digesting food.

Scientists describe the second part with a number called the physical activity level (PAL), so that TDEE = BMR x PAL. If you eat about your TDEE, your weight stays roughly the same. Eat less and you lose weight; eat more and you gain it.

For reference, the NHS says an average man needs about 2,500 calories a day and an average woman about 2,000 to stay at a healthy weight. Your own figure can be well above or below that, which is why a personal estimate is more useful.

How This Calculator Works Out Your Calories

It multiplies your Mifflin-St Jeor resting calories by a UK SACN activity level of 1.49 to about 2.2.

The calculator is for adults aged 18 and over.

Resting calories use the Mifflin-St Jeor equation, published in 1990 from measurements in 498 healthy adults of normal weight and with obesity:

• Men: 10 x weight (kg) + 6.25 x height (cm) - 5 x age (years) + 5

• Women: 10 x weight (kg) + 6.25 x height (cm) - 5 x age (years) - 161

Activity uses the UK reference values from the Scientific Advisory Committee on Nutrition (SACN), which advises the government on diet. Its 2011 report on energy is based on studies that measured how many calories people really burn (the doubly labelled water method), not on activity questionnaires:

• Less active than most: PAL 1.49

• About average: PAL 1.63, the median for adults

• More active than most: PAL 1.78

• Very active: about 2.2, for intense daily training

SACN found that adults leading sustainable lifestyles fall between about 1.38 for the most sedentary and 2.5 for the most active, and that values as low as 1.27 are not thought to be sustainable. Some calculators use 1.2 for a desk job, which is below even that, so they tend to underestimate how much you burn.

How Big Should Your Calorie Deficit Be?

The NHS suggests around 600 calories a day less than your TDEE; the calculator also offers a gentler 300.

The NHS advises: "Aim to reduce your intake by around 600 calories a day. This is a safe and sustainable way to lose weight." The calculator offers that, and a gentler 300 calories a day for people who would rather go more slowly.

It never suggests eating fewer calories than your resting rate. If a 600 calorie cut would take you below it, the calculator shows the smaller deficit instead.

If you have a health condition, take regular medicines (including insulin or other diabetes medicines) or have had an eating disorder, speak to your GP before cutting calories.

How Long Will It Take to Lose Weight?

Weight loss slows as you get lighter: a lasting 600 calorie cut levels off about 25 kg lower, half in the first year.

The NHS suggests aiming to lose weight steadily, at about 0.5 to 1 kg (1 to 2 lb) a week. On a fixed intake, losses start near that pace and slow down over time, because a lighter body burns fewer calories, so the same intake creates a smaller deficit. Researchers writing in The Lancet in 2011 showed that assuming the same weekly loss for months on end overestimates how much weight people lose.

The same paper gives a simpler rule of thumb, which the calculator uses: every lasting cut of 100 kJ (about 24 calories) a day leads, over time, to about 1 kg less body weight. It takes about a year to reach half of that change, and most of the rest comes over the following two years.

In practice:

• Eating 600 calories a day below your TDEE and sticking to it, your weight would level off about 25 kg (around 4 stone) lower, with about half of that in the first year.

• Eating 300 calories a day less, it would level off about 12.5 kg (around 2 stone) lower.

These are averages across many people. To keep losing beyond that point, you would need to eat a little less again, move more, or both. Recalculating your TDEE every few months, at your new weight, keeps the numbers honest.

Calories When Breastfeeding or Pregnant

Exclusive breastfeeding adds about 330 calories a day for six months; weight loss in pregnancy is not advised.

Breastfeeding. SACN recommends about 330 extra calories a day for the first six months of feeding your baby only breast milk. After that, it says the extra energy you need depends on your own body composition and how much breast milk your baby takes, so there is no single figure. The calculator adds the 330 calories when you choose exclusive breastfeeding, and offers only the gentler deficit. The NHS says you do not need a special diet while breastfeeding. Speak to your health visitor or GP before cutting calories.

Pregnancy. SACN states that weight loss during pregnancy is not advised. It adds about 190 calories a day in the last three months only. If you choose pregnancy, the calculator shows your maintenance calories and no deficit.

When a Calorie Deficit Is Not Enough

If diet and activity have not worked, a GP or pharmacist can discuss other options, including licensed medicines.

Eating less and moving more is the starting point for everyone, and for many people it is enough. Some people find their weight does not shift, or comes back. If that is you, there are other options to discuss with a GP or pharmacist.

Weight loss medicines such as Wegovy (semaglutide) and Mounjaro (tirzepatide) are licensed in the UK for adults with a BMI of 30 or more, or 27 or more with a weight-related health condition. They are used alongside a reduced-calorie diet and more physical activity, not instead of them. A prescriber checks whether they are suitable for you, including if you are pregnant, planning a pregnancy or breastfeeding.

Scientific References

1. NHS Better Health. Calorie counting.
2. NHS. Understanding calories.
3. NHS. Overweight and obesity in adults: treatment.
4. Scientific Advisory Committee on Nutrition. Dietary Reference Values for Energy (2011).
5. Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51:241-7.
6. Hall KD et al. Quantification of the effect of energy imbalance on bodyweight. Lancet 2011;378:826-37.
7. NHS. Breastfeeding and diet.
8. Wegovy 2.4 mg, FlexTouch solution for injection in pre-filled pen - Summary of Product Characteristics.
9. Mounjaro KwikPen solution for injection in pre-filled pen - Summary of Product Characteristics.

Frequently Asked Questions