How Many Calories Should I Eat to Lose Weight? Deficit Explained

The short answer

To lose weight, eat fewer calories than your body uses each day. Estimate your daily use (called TDEE, total daily energy expenditure), then subtract a moderate amount. The NHS suggests cutting about 600 calories a day as a safe, sustainable approach; the Lazyblink Calorie Calculator uses a 500-calorie deficit when you choose "Lose weight". Both are starting points to adjust after a few weeks, not exact predictions.

This guide is general information, not medical advice. If you are pregnant, under 18, have a medical condition or take medication that affects appetite or weight, speak to a doctor or dietitian before changing how much you eat.

Step 1: Estimate how much energy you use

Your body burns energy in two broad ways:

• BMR (basal metabolic rate): what you would burn at complete rest, keeping your organs working.
• Activity: everything else, from walking around to exercise.

The calculator estimates BMR with the Mifflin–St Jeor equation, using your sex, age, weight and height:

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

It then multiplies BMR by an activity factor to estimate TDEE:

Activity level in the calculator	Multiplier
Sedentary (no exercise)	1.2
Light (1–3 days/week)	1.375
Moderate (3–5 days/week)	1.55
Very active (6–7 days/week)	1.725
Extra active (athlete)	1.9

Step 2: Subtract a moderate deficit

Your weight-loss target is TDEE minus the deficit. In the calculator, choosing Lose weight subtracts 500 calories and labels the result as about 0.5 kg a week. Choosing Maintain shows TDEE itself.

A deficit of 500 to 600 calories a day is a common, moderate choice. Bigger cuts are harder to stick to and can leave you hungry and tired, which usually ends the diet early.

Worked examples

These were calculated with the same formulas the calculator uses.

Example 1: woman, 30 years, 65 kg, 160 cm, light activity

• BMR: 10 × 65 + 6.25 × 160 − 5 × 30 − 161 = 1,339 kcal
• TDEE: 1,339 × 1.375 = about 1,841 kcal
• Target with a 500 deficit: about 1,341 kcal a day
• With the NHS's 600 suggestion it would be about 1,241 kcal a day

Example 2: man, 35 years, 80 kg, 175 cm, moderate activity

• BMR: 10 × 80 + 6.25 × 175 − 5 × 35 + 5 = about 1,724 kcal
• TDEE: 1,724 × 1.55 = about 2,672 kcal
• Target with a 500 deficit: about 2,172 kcal a day

The same man if he is sedentary

• TDEE: about 2,069 kcal
• Target: about 1,569 kcal a day

The difference between examples 2 and 3 is about 600 calories a day, purely from the activity setting. Choosing the right activity level matters as much as the deficit itself.

Person	TDEE	Target (TDEE − 500)
Woman, 65 kg, light activity	1,841	1,341
Man, 80 kg, moderate activity	2,672	2,172
Man, 80 kg, sedentary	2,069	1,569

How to use the Calorie Calculator

Open the Calorie Calculator.

Choose Metric (kg/cm) or Imperial (lbs/in) first, then set the sliders. Switching units does not convert values you have already set, so check the numbers after switching.

Select your sex and set age, weight and height with the sliders.

Pick the activity level that matches a typical week, not your best week.

Choose Lose weight.

Read three numbers: BMR, TDEE and Target. The Target is your starting daily calorie goal.

The calculator also suggests a protein, fat and carbohydrate split for the target. It sets protein at 1.6 g per kg of body weight, fat at 25% of the target calories, and the rest as carbohydrate. For example 2, that is 128 g protein, 60 g fat and 280 g carbohydrate. Treat this as one reasonable split, not a requirement.

Step 3: Check your progress and adjust

Equations give estimates. Two people with the same age, height and weight can burn quite different amounts. So:

Follow your target consistently for two to four weeks.

Weigh yourself at the same time of day, on the same scale, a few times a week, and look at the average rather than any single day.

If your average weight is not falling, reduce your target a little or increase activity. If it is falling faster than you intended, or you feel unwell, eat more.

Recalculate after a noticeable change in weight, because a lighter body uses less energy.

Common mistakes

• Overestimating activity. Choosing "Very active" because you go to the gym three times a week can add hundreds of calories to your TDEE. Most office workers who exercise a few times a week fit "Light" or "Moderate".
• Eating back exercise calories twice. If you selected an activity level that includes your workouts, do not also add the calories your watch says you burned.
• Underestimating food. Oil, drinks, sauces and snacks are easy to miss. If you track food, include them.
• Going too low. Very large deficits are hard to keep up and can make it difficult to get enough nutrients. Speak to a professional if you are considering a very low calorie diet.
• Expecting a straight line. Weight changes day to day with water, salt and digestion. Judge progress over weeks.

Related tools and guides

• Check what your current weight means for your height with the BMI Calculator, keeping in mind BMI's limitations.
• If a food label shows energy in kilojoules, convert it with the guide to reading kJ and kcal on food labels.
• For more on how TDEE works, see Calorie Calculator: How to Find Your TDEE.