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Nutrition Crash Course

FREE TOOL: Get your personalised macro targets for weight loss. No sign-up, nothing stored.

Macro Calculator for Weight Loss

Estimate a modest calorie deficit and the protein, carbs and fat that go with it, with every step shown. For adults only.

Enter Your Details

All fields are required. Nothing you enter is stored or sent anywhere.

First, two safety questions
Are you pregnant or breastfeeding?
Are you managing a medical condition with your diet, taking medicine affected by what you eat, or have you had an eating disorder?
Sex used in the equation

Pick the level closest to a typical week, not your most active one.

A common modest starting point.

Lower end of the 1.2–2.0 g/kg range sports bodies use for regular training.

Which activity level fits me?
  • Very low activity (× 1.40): Mostly sitting or lying, little walking, no regular exercise.
  • Sedentary or light (× 1.53): Desk-based work, some walking, little planned exercise.
  • Active or moderately active (× 1.76): On your feet a lot, or a desk job plus regular exercise most days.
  • Vigorous (× 2.25): Hard physical work or strenuous exercise for several hours most days.

Your Daily Targets

Answer every question above and press Calculate My Macros. Your estimate will appear here.

Calories
—Awaiting your details
Protein
—Awaiting your details
Carbs
—Awaiting your details
Fat
—Awaiting your details

Ready to Put Your Macros Into Practice?

See the calories, protein, carbs and fat per serving in meals you actually cook, using USDA FoodData Central values for each ingredient. Free, with nothing to sign up for.

Explore Recipe Nutrition Calculator

Why Use a Macro Calculator?

  • See every step. The equation, activity multiplier and macro split are shown with your own numbers, so you can check the working rather than trust a black box.
  • A well-tested starting point. It uses Mifflin-St Jeor, which a systematic review rated the most reliable of the common resting-energy equations. It is still an estimate to adjust over a few weeks, not a promise of results.
  • Modest, private, in your units. Deficits are 250 or 500 kcal a day, it won’t show targets under 1,200 kcal, and it works in kg, lb or stones and cm or feet. Nothing is saved.

What your result means

Maintenance is the estimated number of calories that would keep your weight about the same. Your target is that estimate adjusted for your goal. Both are starting points from an equation, not measurements of your body.

Use the target for a few weeks, weigh yourself regularly under similar conditions, and adjust if your weight is not moving as you expected. If you need a large change or feel unwell, stop and speak to a GP or registered dietitian.

How the numbers are built: resting energy (Mifflin-St Jeor) × activity level = maintenance. Then −250 or −500 kcal for weight loss, or +10% for muscle gain. Protein = g/kg × weight; fat = 30% of calories; carbohydrate = the rest. 4/4/9 kcal per gram of protein/carbohydrate/fat.

Method and limitations

Resting energy. Mifflin-St Jeor: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years), then +5 for men or −161 for women. It was developed in 498 healthy adults aged 19–78, including people with obesity.

Activity. Multipliers come from the FAO/WHO/UNU physical activity level bands: 1.40–1.69 sedentary or light, 1.70–1.99 active, 2.00–2.40 vigorous. Choosing a level is the biggest source of error, so pick the one closest to a typical week, not your best week.

Uncertainty. The range shown is ±10% of maintenance, the accuracy threshold used in the 2005 review. Some people fall outside it. The equation doesn't know your body composition, medicines or health conditions.

Macros. Fat is fixed at 30% of calories, inside EFSA’s 20–35% adult range. Carbohydrate is what remains, and the result tells you if it falls outside EFSA’s 45–60% range. Protein uses your current weight, which can overstate needs at higher body weights.

Sex. The equation has separate female and male versions. If neither fits your body, or you take hormone treatment, ask a clinician which estimate suits you.

Who shouldn’t use it

Don’t use this calculator if you are under 18, pregnant or breastfeeding, managing a medical condition such as diabetes or kidney disease with diet, taking medicine affected by what you eat, or have had an eating disorder. Older adults may also have different needs. In these situations a doctor or registered dietitian can give advice that fits you.

Common Questions

How many calories should I eat to lose weight?

There is no single right number. This calculator estimates the calories you need to stay the same weight, using the Mifflin-St Jeor equation and your activity level, then takes away 250 or 500 kcal a day. Treat the result as a starting point and adjust it based on how your weight actually changes over several weeks.

Is the Mifflin-St Jeor equation accurate?

A 2005 systematic review found it estimated resting metabolic rate within 10% of the measured value more often than other common equations. Larger errors still happen for some people, and older adults and some ethnic groups were underrepresented in the research.

How are the macros worked out?

Protein is set from your body weight, fat is set at 30% of calories (inside EFSA's 20–35% reference range), and carbohydrate makes up the rest. Protein and carbohydrate are counted at 4 kcal per gram and fat at 9 kcal per gram.

Why won't it show a target below 1,200 kcal?

The NHS describes diets under 800 or 1,200 calories a day as very low calorie diets. They are not suitable or safe for everyone and are followed with support from a dietitian. If your estimate falls below that, speak to a GP or registered dietitian.

How fast will I lose weight?

The calculator doesn't predict a rate. Weight change tends to slow over time as the body adapts, so simple rules that turn a daily deficit into a fixed weekly loss overstate long-term results. The NHS suggests aiming to lose 0.5 to 1 kg (1 to 2 lb) a week.

Who should not use this calculator?

Anyone under 18, anyone who is pregnant or breastfeeding, and anyone managing a medical condition with their diet, taking medicine affected by diet, or who has had an eating disorder. A doctor or registered dietitian can give advice that fits you.

Is my information saved?

No. The calculation runs in your browser. Nothing you enter is stored or sent to a server.

Method and sources