How Many Calories Should I Eat to Lose Weight? UK Guide

For most healthy adults, safe weight loss comes from a daily calorie deficit of around 500–600 kcal below your maintenance level (TDEE), in line with NHS and NICE guidance. As a general population reference, adults need roughly 2,000 kcal a day for women and 2,500 kcal for men to maintain their current weight, though your personal number depends on your age, height, weight, and activity level. NHS guidance advises not going below 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision.

At CalZone, we've put together this guide to help you understand where these numbers come from and how to calculate your own — not as a diet plan, but as a starting point for a conversation with your GP or a registered dietitian if you're planning meaningful changes to your diet.

Understanding Calorie Deficit

Weight loss happens when you consistently consume fewer calories than your body uses — known as a calorie deficit. Your body then draws on stored energy (largely fat) to make up the difference. The size of a sensible deficit, and how you achieve it, matters far more than extreme or rapid cuts to intake.

The NHS and the National Institute for Health and Care Excellence (NICE) both point to the same broad range: a deficit of around 500–600 kcal per day is generally considered safe and sustainable for most healthy adults, without excessive muscle loss, nutritional deficiencies, or the rebound weight regain that's common after very restrictive diets.

Step 1: Work Out Your Maintenance Calories (TDEE)

Before you can calculate a deficit, you need to know your Total Daily Energy Expenditure (TDEE) — the number of calories your body uses in an average day, including your metabolism, daily movement, and exercise.

TDEE is commonly estimated in two steps:

1. Calculate your Basal Metabolic Rate (BMR) — the energy your body needs at complete rest, using the Mifflin-St Jeor equation:
   • Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
   • Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
2. Multiply your BMR by an activity factor:

Worked Example

A 30-year-old woman, 165cm tall, weighing 65kg, who is moderately active:

• BMR = (10 × 65) + (6.25 × 165) − (5 × 30) − 161 = 650 + 1,031.25 − 150 − 161 ≈ 1,370 kcal/day
• TDEE = 1,370 × 1.55 (moderately active) ≈ 2,124 kcal/day

This is roughly what she'd need to eat to maintain her current weight.

Step 2: Apply a Safe Deficit

Once you know your TDEE, a safe daily calorie target for weight loss is usually your TDEE minus 500–600 kcal:

• 2,124 (TDEE) − 500 = 1,624 kcal/day for a target loss of roughly 0.5kg per week.
• 2,124 (TDEE) − 600 = 1,524 kcal/day for a slightly faster, still sustainable rate.

A rough rule of thumb: roughly 3,500 kcal of deficit equates to about 0.45kg (1lb) of fat loss, so a 500 kcal/day deficit works out to approximately 0.5kg lost per week.

NHS and NICE Guidance at a Glance

Why Going Too Low Is Counterproductive

It might seem logical that a bigger deficit means faster results, but NHS and NICE guidance is consistent that dropping much below the recommended range tends to backfire:

• Muscle loss — severe restriction can cause your body to break down muscle tissue alongside fat, which actually lowers your metabolic rate over time.
• Nutritional deficiencies — very low intakes make it hard to get enough protein, vitamins, and minerals from food alone.
• Metabolic adaptation — prolonged, severe restriction can cause your body to adapt and slow its energy use, contributing to frustrating plateaus.
• Difficulty sustaining it — diets that feel extreme are harder to stick to long-term, which is often why weight lost quickly tends to come back.

This is why the NHS specifically advises against very low-calorie diets (typically defined as under 800 kcal/day) without medical supervision.

Practical Ways to Build a Sensible Deficit

Rather than cutting calories dramatically, small, sustainable changes tend to work better over time:

• Increase vegetables and fibre — high-volume, lower-calorie foods that help you feel fuller.
• Cut back on sugary drinks — switching to water or sugar-free alternatives can save a meaningful number of calories.
• Reduce portion sizes gradually — rather than eliminating entire food groups.
• Add regular movement — the NHS recommends at least 150 minutes of moderate-intensity activity per week.
• Prioritise protein — helps preserve muscle mass while you're in a calorie deficit.

Who Should Speak to a GP or Dietitian First

Calculating a general deficit using the formulas above is a reasonable starting point for most healthy adults, but you should speak to your GP or a registered dietitian before making significant changes to your calorie intake if:

• You are pregnant or breastfeeding.
• You have diabetes, particularly if you take insulin or certain other medications.
• You have, or have previously had, an eating disorder.
• You have an existing health condition that affects your diet or metabolism.

Tracking Progress Beyond the Scale

Body weight naturally fluctuates day to day due to water retention, hormones, and food volume. Relying on the scale alone can be misleading. Consider tracking progress in a few different ways:

• Weekly averages rather than single daily readings, to smooth out normal fluctuation.
• How your clothes fit, which often reflects body composition changes the scale doesn't capture.
• Energy levels and sleep quality, which tend to improve with a sensible, sustainable approach.