How do I work out my calorie deficit?
Work out what you burn, then eat about 600 calories less. The NHS calls that safe and sustainable. But the gap shrinks as you lose weight, so you need to redo the sum.
On this page
How do I work out my calorie deficit?
A deficit means you eat fewer calories than you burn. The NHS says to cut around 600 calories a day. It calls that a safe and sustainable way to lose weight.
Your sum has three steps. It is for adults.
Work out what you burn at rest and times it by how active you are. Then take away 600.
For step 1, use the Mifflin-St Jeor formula. Use your weight in kg, height in cm and age in years:
- Men: 10 × weight, plus 6.25 × height, minus 5 × age, plus 5.
- Women: 10 × weight, plus 6.25 × height, minus 5 × age, minus 161.
| Step | Person A: woman, 45, 165 cm, 75 kg | Person B: man, 40, 180 cm, 90 kg |
|---|---|---|
| 1. Burn at rest | 1,395 | 1,830 |
| 2. Times 1.63 | 2,274 | 2,983 |
| 3. Minus 600 | 1,674 a day | 2,383 a day |
Sources: Mifflin-St Jeor; SACN; NHS
Do the same sum with your own numbers. Your step 3 number is your daily calorie goal.
Rather skip the maths? The NHS way is to total a normal day of food and drink, then cut around 600 from that.
How many calories do I burn a day?
On average, the NHS says women use around 2,000 calories a day and men around 2,500. Yours could be different based on your age, weight, height and exercise.
To get closer, times your step 1 number by an activity number. SACN, the experts who advise the UK government on food, use three.
| How active you are | Times your step 1 by | Person A burns |
|---|---|---|
| Less active than most | 1.49 | 2,079 |
| About average | 1.63 | 2,274 |
| More active than most | 1.78 | 2,484 |
Source: SACN
Not sure? Pick average. Half the adults in SACN’s data were above 1.63 and half were below.
Every formula is a best guess. A review found Mifflin-St Jeor landed within 10% of a measured result for more people than three other common ones. It can still miss for one person, and older adults and some ethnic groups were less tested.
So treat your number as a starting point. Your scales over a few weeks will show whether it’s right.
How low should my calories go?
Not to 1,200 or below on your own.
NICE sets NHS treatment rules. It says diets of 800 to 1,200 calories a day are only for some people with obesity, or overweight with type 2 diabetes. They need long-term support from a specialist service.
- Below 800 kcal a dayNICE: very low. Specialist service only.
- 800 up to 1200 kcal a dayNICE: low. Only with specialist support.
- Above 1200 kcal a dayAbove NICE’s low-calorie diet.
Source: NICE NG246
Under 800 is for people with obesity whose doctor has assessed a need to lose weight fast, such as to make surgery safer. NICE says not to use either diet as a long-term plan.
Smaller, older and less active people can land low. Take a 55-year-old woman, 160 cm and 60 kg, who is less active. She burns about 1,734, and minus 600 gives 1,134.
If your step 3 lands at 1,200 or below, cut less and ask your GP. Check your BMI number too.
Why does my calorie deficit stop working?
Because you get lighter. A lighter body burns less, so the same meals leave a smaller gap.
Sources: Mifflin-St Jeor; SACN
That’s why you redo the sum. When your weight drops, put your new weight into step 1.
Your body adapts too. An old rule says a set cut keeps losing the same amount each week. A 2011 study in The Lancet, a medical journal, says it ignores changes in the energy you burn at rest and on the move.
In their model, a 100 kg inactive man who cut 480 calories a day levelled off at about 75 kg. It took roughly a year to lose half of that 25 kg.
A model is a forecast, not a promise. Track your weight loss percentage to see your real pace.
How do I track my calorie deficit?
Count a normal day first. The NHS says to total what you eat and drink, then find where to cut around 600.
Where to find your 600 a day
- Cut around 100 at breakfast. Weigh your cereal and skip jam and chocolate spreads.
- Cut around 200 at lunch. Check labels and choose water or sugar-free drinks.
- Cut around 200 at dinner. Limit ready meals and takeaways, and cook from scratch.
- Cut around 100 from snacks. Swap crisps and chocolate for fruit or plain popcorn.
- Weigh portions before cooking at first. A 75 g pack portion of rice is 260 calories, but 150 g is 520.
- Log everything, including drinks, cooking oil, toppings and sauces.
Source: NHS: calories and weight loss
The free NHS Weight Loss Plan app can set a daily calorie goal and track it for you.
Weigh yourself regularly and aim to lose 0.5 to 1 kg a week. Drinks count too, so see the lowest calorie alcoholic drinks. To keep your strength as you lose, read keeping muscle as you lose weight.
When to speak to a GP
Talk to a GP before you start cutting calories, or as soon as you can, if:
- You have a medical condition, a special diet for your health, or an eating disorder now or in the past. The NHS says to talk to a GP first.
- You worry a lot about your weight or shape, eat very little, make yourself sick, take laxatives (products that make you poo) or exercise too much. These can be signs of an eating disorder.
- You keep losing weight without changing your diet or exercise. Go as soon as possible if you have other symptoms too.
- Your step 3 lands at 1,200 or below, or you want help to lose weight.
A GP can refer you to a weight management programme. You can also call the Beat eating disorder helpline on 0808 801 0677.
Pregnant with a BMI of 30 or more? The NHS says don’t try to lose weight while you’re pregnant.