Macro Calculator UK
Calculate your daily protein, carbs and fat targets based on your TDEE and goals.
Last updated: February 2026 — Mifflin-St Jeor formula, ISSN macro guidelines
Calculate Your Macros
Uses the Mifflin-St Jeor formula to calculate your TDEE, then applies your goal macro split.
Quick Preset Splits:
Understanding Your Macronutrients
Macronutrients — protein, carbohydrates, and fat — are the three main nutrients your body requires in large quantities for energy and function. Unlike micronutrients (vitamins and minerals needed in small amounts), macros are the primary fuel sources that determine your body composition, energy levels, and performance.
The concept of IIFYM (If It Fits Your Macros) has become popular because it provides flexibility while still maintaining the structure needed to reach body composition goals. Rather than following rigid meal plans, you track your macronutrient grams and have freedom to choose which foods fill those targets — making it more sustainable long-term than traditional dieting approaches.
The Mifflin-St Jeor Formula Explained
This calculator uses the Mifflin-St Jeor equation to estimate your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest. Developed in 1990, it remains the most validated BMR formula for most non-athlete populations:
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
Your TDEE (Total Daily Energy Expenditure) is then calculated by multiplying your BMR by an activity factor. The calorie target is adjusted from TDEE based on your goal: −500 calories for weight loss, 0 for maintenance, or +300 for lean muscle gain.
Macro Split Presets Explained
| Preset | Protein | Carbs | Fat | Best For |
|---|---|---|---|---|
| Balanced | 30% | 40% | 30% | General health and maintenance |
| High Protein | 35% | 40% | 25% | Weight loss & muscle preservation |
| Low Carb | 35% | 20% | 45% | Fat adaptation, insulin management |
| Ketogenic | 25% | 5% | 70% | Therapeutic, strict fat loss |
| Athletic/Endurance | 25% | 55% | 20% | Endurance sports, high-volume training |
Role of Each Macronutrient
Protein — The Building Block (4 cal/g)
Protein is composed of amino acids, nine of which are essential (cannot be made by the body and must come from food). It supports muscle protein synthesis, immune function, enzyme production, hormone synthesis, oxygen transport (haemoglobin), and tissue repair. During weight loss, high protein intake preserves muscle mass and keeps you fuller for longer due to its high satiety value.
During muscle gain phases, adequate protein ensures the raw materials are available for hypertrophy. UK sources: chicken, fish, eggs, dairy, legumes, tofu.
Carbohydrates — The Primary Fuel (4 cal/g)
Carbohydrates are broken down into glucose, which is the preferred fuel for the brain, central nervous system, and high-intensity exercise. Glycogen (stored glucose in muscles and liver) directly fuels anaerobic performance like weight training and sprinting. Complex carbohydrates (wholegrains, oats, sweet potato, legumes) provide sustained energy, fibre, and micronutrients.
Simple carbohydrates (fruit, white rice, sports drinks) provide rapid energy useful around training. UK guidelines recommend 50% of energy from carbohydrates for most adults.
Fat — The Essential Regulator (9 cal/g)
Dietary fat is essential for absorbing fat-soluble vitamins (A, D, E, K), producing steroid hormones (including testosterone and oestrogen), maintaining cell membrane integrity, and supporting brain and nervous system function. A minimum of 0.8–1.0g fat per kg bodyweight is recommended to maintain hormonal health — going below this can suppress testosterone and disrupt the menstrual cycle. Prioritise unsaturated fats (olive oil, nuts, avocado, oily fish) over saturated fats. Trans fats (partially hydrogenated oils) should be minimised.
Calorie Adjustments for Your Goal
Once you know your TDEE, adjusting calories appropriately for your goal is the foundation of body composition change. The adjustment should be moderate and sustainable — extreme deficits or surpluses create problems with muscle loss, fat gain, and metabolic adaptation.
Weight Loss
TDEE − 300 to 500 cal/day
Expected loss: 0.3–0.5kg/week
Preserves muscle with high protein
Maintenance
Eat at TDEE
Stable weight and body composition
Ideal for performance goals
Muscle Gain
TDEE + 200–400 cal/day
Expected gain: 0.2–0.5kg/week
Minimises fat gain (lean bulk)
These are starting points. Monitor your body weight weekly (same day, same time of day) and adjust by 100–200 calories if results don't match expectations after 2–3 weeks. Body weight fluctuates 1–2kg daily due to water, food, and hormones — focus on weekly averages rather than daily readings.
How the Macro Calculator Works
This calculator uses established health formulas and UK-specific reference ranges to provide useful estimates. While online calculators are helpful for general guidance, they should not replace professional medical advice. Always consult your GP or a qualified health professional for personalised health assessments.
UK health guidelines are published by the NHS, Public Health England, and NICE (National Institute for Health and Care Excellence). This tool aligns with these official guidelines where applicable, providing results relevant to the UK population.
Key Information
The NHS recommends at least 150 minutes of moderate-intensity activity per week for adults, or 75 minutes of vigorous activity. A healthy BMI range for adults is 18.5 to 24.9. The UK Chief Medical Officers advise that both men and women should not regularly drink more than 14 units of alcohol per week. Calorie guidance suggests approximately 2,000 kcal per day for women and 2,500 kcal for men, though individual needs vary.
Example Calculation
A 30-year-old female who is 165cm tall and weighs 65kg would have a BMI of 23.9, which falls within the healthy range. Her estimated Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation would be approximately 1,387 kcal per day, rising to around 1,910 kcal with moderate activity.
Source: Based on NHS and Public Health England guidelines. Last updated March 2026.
Frequently Asked Questions
What are macros (macronutrients)?
Macronutrients are the three main nutrients your body needs in large amounts: protein, carbohydrates, and fat. Protein provides 4 calories per gram and is essential for muscle building and repair. Carbohydrates also provide 4 calories per gram and are your body's primary energy source.
Fat provides 9 calories per gram and is vital for hormone production, vitamin absorption, and brain function. Tracking macros means monitoring the grams of each macronutrient you consume daily, giving you more nutritional control than simply counting calories.
What is the best macro split for weight loss?
For weight loss, a recommended macro split is approximately 30–35% protein, 35–40% carbohydrates, and 25–30% fat. Higher protein intake during a calorie deficit helps preserve muscle mass, increases satiety, and has a higher thermic effect. The exact split is less critical than maintaining an appropriate calorie deficit — typically 300–500 calories below your TDEE for sustainable fat loss of 0.5–1kg per week.
What macro split should I use for muscle gain?
For muscle gain (lean bulking), a recommended macro split is approximately 25–30% protein, 45–55% carbohydrates, and 20–30% fat. Protein should be 1.6–2.2g per kg bodyweight. Carbohydrates are prioritised higher than in weight loss because they fuel intense resistance training sessions and support recovery. A calorie surplus of 200–400 calories above TDEE promotes gradual muscle gain while minimising fat accumulation.
How do I track macros as a UK resident?
To track macros in the UK, use apps like MyFitnessPal, Cronometer, or Nutracheck (UK-specific). These apps have extensive UK food databases including supermarket-specific entries for Tesco, Sainsbury's, Waitrose, and Aldi. Use a food scale for accuracy — volume measurements are unreliable.
Read food labels: UK labels show protein, carbohydrates (including sugars), and fat per 100g and per serving. Track everything consistently for at least 2–3 weeks before making adjustments.
How many calories is 1g of each macronutrient?
Each macronutrient provides a specific calorie value: Protein = 4 calories per gram, Carbohydrates = 4 calories per gram, Fat = 9 calories per gram. This means fat is more than twice as calorie-dense as protein or carbohydrates by weight. To calculate calories from macros: multiply protein grams by 4, carb grams by 4, and fat grams by 9, then sum all three. For example, 150g protein + 200g carbs + 60g fat = 600 + 800 + 540 = 1,940 calories.
Should I count net carbs or total carbs?
In the UK, food labels display total carbohydrates which includes fibre. For most dietary approaches (calorie counting, IIFYM), use total carbohydrates as shown on UK food labels. Net carbs (total carbs minus fibre) is primarily used in ketogenic diet tracking.
Unless you're following a strict ketogenic diet (keeping net carbs below 20–50g daily), there's no need to subtract fibre. UK labels already separate "of which sugars" within total carbohydrates, useful for monitoring sugar intake separately.
How accurate is the Mifflin-St Jeor equation?
The Mifflin-St Jeor equation is considered the most accurate BMR formula for most people, with studies showing it estimates within 10% of measured metabolic rate for approximately 82% of individuals. It tends to slightly overestimate for obese individuals and underestimate for very muscular people. Use the calculator output as a starting point, then monitor your weight for 2–3 weeks and adjust calories by 100–200 based on results. If weight isn't changing as expected after 3 weeks of consistent tracking, recalculate using actual results.