Macro calculator: work out your calories, protein, carbohydrate and fat (a UK guide for men)

This calculator estimates your daily energy need with the equations the UK's Scientific Advisory Committee on Nutrition (SACN) uses. [1] It then takes off around 600 kcal a day, the reduction the NHS suggests for losing weight. [2] It shows the protein, fat, carbohydrate and fibre that go with the result.

Kcal is kilocalories, the calories on food labels. Macros, short for macronutrients, are the three nutrients that supply energy: protein, carbohydrate and fat.

Every figure is an estimate for an average person of your sex, age, height, weight and activity level. It is not a measurement. The UK figures behind it describe populations, not any one man. [1]

Enter your details below. The sections after the calculator explain where each number comes from and how much to trust it.

What are your macros?

The calculator shows an estimated daily energy need, a target 600 kcal below it, and the protein, fat, carbohydrate and fibre that fit that target. [1] [2]

How do you use it?

Enter your sex, age, height, current weight and activity level. The three activity levels are SACN's: less active (sedentary), typically active (light activity, SACN's population value) and more active (moderate activity).

How to read the result

The headline is a daily energy target, not a prescription. Protein comes first because the review behind the range expressed it per kilogram of body weight, not as a share of energy. [5]

Fat is a ceiling, so you can eat less than the figure. Carbohydrate is what remains, shown as a range because protein is a range.

If you choose "Maintain", the calculator shows the estimated need itself and builds the macros on that figure. Enter your current weight, not a goal weight.

How does the calculator work?

The calculator follows the method SACN set out in 2011: energy need equals basal metabolic rate multiplied by a physical activity level. [1] Basal metabolic rate (BMR) is the energy your body uses at complete rest. The physical activity level (PAL) is a multiplier for everything else you do in a day.

Step 1: basal metabolic rate

SACN chose the Henry equations, published in 2005 from a database of 10,552 measurements, and used the version that takes both weight and height. [1] [4]

There is one equation per sex for each of three adult age bands: 18 to 30, 30 to 60 and over 60. [1] The calculator places ages 30 and 60 in the older band. That is a convention of ours, because the published tables overlap or leave a gap at those ages. [1] [4]

The result comes out in megajoules a day and is converted at 1 kcal to 4.184 kJ (kilojoules), which is about 239 kcal per megajoule. [1] The exact coefficients sit in the page code beside the calculator, copied from SACN's Table 18.

Step 2: activity level

SACN took the spread of measured activity in a reference population and used three values: [1]

• 1.49 for the less active quarter
• 1.63 for the median
• 1.78 for the more active quarter

SACN describes them in general terms as sedentary, low activity and moderate activity. [1] The median is the default when nothing else is known about a person's activity. [1]

Step 3: the weight-loss target

The NHS advice for losing weight is to reduce your intake by around 600 calories a day, which it calls safe and sustainable. [2] The calculator takes 600 kcal off the estimated need.

NICE, which writes guidance for the NHS, requires an energy deficit but gives no number. [3] It accepts low-fat or low-carbohydrate approaches as ways to reach one. [3]

Step 4: protein

Protein is set at 1.2 to 1.6 g per kilogram of current body weight, the range a 2015 review drew from weight-loss trials. [5] That is a trial range, not UK guidance.

The UK reference nutrient intake is 0.75 g per kilogram, set to prevent deficiency, and the calculator shows it as a baseline. [6] The 1991 UK advice was to stay under twice the reference intake, which is 1.5 g per kilogram. [6] The top of the range sits just above that line.

Step 5: fat

UK guidance puts total fat at no more than 35% of food energy and saturated fat at no more than 11%. [7] The calculator converts both shares to grams at 9 kcal per gram and shows them as ceilings. [9]

The World Health Organization suggests 30% or less for preventing weight gain. [10] It also says most adults need at least 15% to 20% of energy from fat. [10] Those are WHO figures, not UK guidance, and WHO says the 30% figure may not apply to people actively losing weight. [10]

Step 6: carbohydrate and fibre

Carbohydrate is the energy left after protein and fat, divided by 4 kcal per gram. [9] It is arithmetic, not a recommendation.

SACN's population figure of about 50% of energy was set for people keeping a healthy weight. [8] A weight-loss target with higher protein usually lands below it.

Free sugars are sugars added to food and drink, plus those in honey, syrups and fruit juice. They should not exceed 5% of energy. [8]

Adults should eat 30 g of fibre a day. [8] The fibre figure does not change with the deficit.

What does a worked example look like?

Take a man of 42 who is 180 cm tall, weighs 100 kg and picks the typical activity level. His basal metabolic rate from the Henry equation is 8.25 megajoules a day, about 1,970 kcal. [1] Multiplied by 1.63, his estimated need is about 3,200 kcal a day.

Figure	Result	How it is worked out
Estimated daily need	About 3,200 kcal	Basal metabolic rate multiplied by 1.63 [1]
Weight-loss target	About 2,600 kcal	600 kcal a day less [2]
Protein	120 to 160 g	100 kg multiplied by 1.2 and by 1.6 [5]
Fat	Up to 101 g	35% of 2,600 kcal, divided by 9, rounded down [7] [9]
Saturated fat	Up to 31 g	11% of 2,600 kcal, divided by 9, rounded down [7]
Carbohydrate	About 265 to 305 g	The energy left after protein and fat, divided by 4 [9]
Fibre	30 g	The UK figure for adults [8]

The arithmetic is ours, applied to the cited figures. His protein range is 18% to 25% of the target, and carbohydrate is 41% to 47%. Both fall out of the method rather than being chosen.

Which activity level should you choose?

Unless you know you sit at one end, choose the typical level. SACN says that judging which band a person belongs to poses a difficult problem, and the median of 1.63 is its default. [1]

It describes that median as probably a light activity lifestyle. That sits at the upper end of the sedentary-to-light range used by the WHO, FAO and UN University. [1]

SACN's examples help you place yourself. Thirty minutes of moderate activity on five or more days a week adds about 0.15 to the multiplier. [1] That is the step from one band to the next.

An hour of brisk walking a day adds about 0.2, and an hour of jogging a day about 0.4. [1] Those increments assume you do not rest more or eat more to compensate. [1]

If you train hard most days, your need may sit above the top band. The calculator does not model that. A desk job with no exercise is closest to the bottom band, which SACN describes in general terms as sedentary. [1]

Why is the result only an estimate?

Because every figure in the method is a population average applied to one person. SACN says energy needs vary markedly between individuals, and that individuals may require less or more than the reference values. [1] The NHS gives 2,500 kcal a day as a guide for an average man and says yours could differ with age, weight, height and exercise. [11]

How accurate are the equations?

In a test against measured resting metabolic rate in 767 adults, the weight-and-height Henry equations put 73% of people within 10% of their measured figure. [1] Individual errors ran from 33% below to 35% above. [1] In a separate group of overweight and obese adults, 79% were within 10%. [1]

They still mean that about one person in four is more than 10% away from the estimate. Researchers note that baseline energy needs cannot be measured in a free-living person to better than about 5%. [12] The uncertainty is usually much greater unless the specialised doubly labelled water method is used. [12]

What should you do with the uncertainty?

Treat the target as a starting point and let the scales correct it.

The NHS advises aiming to lose 0.5 to 1 kg a week and weighing yourself regularly. [13]

If your weight does not move over a few weeks, your real need is probably lower than the estimate. Your intake may also be higher than you think. If it falls faster than the NHS range, ease the deficit.

Why does it not predict your weekly weight loss?

Because the common rule for doing so is wrong. The idea that a 3,500 kcal deficit always costs one pound of fat ignores the fall in energy use as you get lighter. [12]

Researchers modelled this for a 100 kg man cutting 480 kcal a day. [12] The static rule overstated his first-year weight loss by about 100%. [12]

Their model showed weight loss slowing over time. Roughly half of the eventual change arrives in about a year, and 95% in about three years. [12]

Their rule of thumb applies to an average overweight adult. [12] Each 100 kJ a day cut from intake leads to about 1 kg of eventual weight change. [12] That is about 24 kcal a day per kilogram, worked out by us.

So the calculator gives a target, not a forecast. The NHS rate of 0.5 to 1 kg a week is advice on a safe pace, not a prediction from the deficit. [13]

How low should your target go?

Not below 1,200 kcal a day without professional support. NICE classes 800 to 1,200 kcal a day as a low-energy diet. [3] It says such a diet should be considered only within a specialist weight management service, with long-term support. [3]

Diets under 800 kcal a day are very-low-energy diets, for people with a clinically assessed need to lose weight quickly. [3] NICE says neither should be used as a long-term strategy. [3] It says both must be nutritionally complete, last no more than 12 weeks and come with clinical supervision. [3]

The NHS describes a very low calorie diet as one followed with a dietitian's support. It says such diets are not suitable or safe for everyone. [13]

For that reason the calculator stops if your target would fall below 1,200 kcal. It shows your estimated need and asks you to speak to your GP or a dietitian instead.

NICE also advises against restrictive diets that are nutritionally unbalanced, because they are ineffective in the long term and can be harmful. [3]

How does this compare with the UK reference intake?

The UK reference intake is a different route to a similar place. SACN's estimated average requirement for men is 2,605 kcal a day, which Public Health England caps at 2,500 to help address overweight and obesity. [1] [7] SACN calculated it at a body mass index (BMI) of 22.5, a healthy weight, rather than at current weights. [1]

SACN did that on purpose. It wrote that if overweight groups eat the amount recommended for healthy-weight groups, they are likely to lose weight. [1] For a man with a BMI of 30 and average activity, the reference intake sits about 426 kcal a day below what holds his weight. [1]

This calculator takes the other route: your need at your current weight, minus the NHS reduction of around 600 kcal a day. [2] It does not do both, because that would stack two deficits. For the 180 cm man in the worked example, SACN's route gives about 2,710 kcal and this calculator about 2,600 kcal, by our arithmetic.

When should you recalculate?

Whenever your weight changes by a few kilograms. The equations use your current weight, so a lighter body gives a lower basal metabolic rate and a lower target. [1] That is the slowing effect the modelling study described. [12]

The protein range moves with your weight too, because it is set per kilogram. [5] That is arithmetic on the same rate, not a new finding. A 100 kg man who reaches 90 kg would see his range move from 120 to 160 g down to 108 to 144 g.

Weighing yourself regularly, as the NHS suggests, tells you when to re-enter your figures. [13] NICE lists self-monitoring of weight among the components of effective weight management. [3] For what the three macros are and why they matter, see what are macros.

Frequently asked questions

Is the macro calculator accurate for me?

No calculator is. The result is an estimate built from population averages, and individuals may require less or more than the reference values. The Henry equations put about three people in four within 10% of their measured resting rate.

Errors for one person run up to a third either way. Use the result as a starting point and weigh yourself regularly. Adjust if your weight moves faster or slower than 0.5 to 1 kg a week.

Why does the calculator ask for my sex and age?

Because the Henry equations have a separate line for each sex and for three adult age bands. Basal metabolic rate falls with age and differs between men and women at the same weight and height.

The per-kilogram protein range and the 30 g fibre figure are the same for men and women. The fat ceiling is a share of your energy target, so the grams follow it.

Should I add back the calories I burn exercising?

No. The activity level already covers your exercise. If you train regularly, pick the more active band rather than adding workouts on top. Otherwise you count the same activity twice.

SACN's examples give a sense of scale: 30 minutes of moderate activity on five days a week is one step up the bands.

Is cutting 600 kcal a day right for everyone?

The 600 kcal figure is a reduction, not an amount to eat. The NHS advice is to eat around 600 calories a day less than you do now, and it calls that safe and sustainable. The calculator takes that 600 kcal off your estimated daily need and shows what is left, never a target below 1,200 kcal a day.

No UK source scales the reduction to body size, so the calculator uses the same 600 kcal for everyone. If that reduction feels too much or too little, the scales and a clinician are better guides than the arithmetic. NICE asks for an energy deficit without naming a number, and says diets that keep a deficit should come with support and follow-up.

Why is my carbohydrate figure below the UK 50%?

Because the calculator sets protein by body weight first and fat at its ceiling, and carbohydrate takes what is left. SACN's 50% figure is a population average for people maintaining a healthy weight, not a rule for a weight-loss target.

NICE accepts low-fat or low-carbohydrate approaches as ways to make an energy deficit. If you eat less fat than the ceiling, your carbohydrate figure rises.

Why is protein shown as a range?

Because the review behind it gave a range of 1.2 to 1.6 g per kilogram a day, drawn from trials rather than from UK guidance. The UK reference intake of 0.75 g per kilogram is shown beside it as the baseline that prevents deficiency.

For protein across the day, and what 30 g looks like on a plate, see how much protein you need to lose weight.

What if I am on a prescribed weight-loss treatment?

Follow the dietary advice of the clinician who prescribes it. The calculator does not account for any treatment.

If the target or the protein range is hard to reach, raise it with your clinician rather than changing it yourself.

HeMed provides clinician-led weight management. This page is general health information, not medical advice. If you are worried about symptoms, speak to your GP, or use NHS 111.

Next step: see what the HeMed blood test measures.

Sources (13)

1. Scientific Advisory Committee on Nutrition (SACN), "Dietary Reference Values for Energy", 2011: Summary paragraphs S31 to S47, paragraphs 11, 118 to 127, 160 to 165, 177 to 181 and 260 to 263, Tables 10 to 13, 16, 18 and 20, and Appendix 4. assets.publishing.service.gov.uk, SACN_Dietary_Reference_Values_for_Energy.pdf. Accessed 28 October 2026.
2. NHS Better Health, "Calories and weight loss". nhs.uk/better-health/lose-weight/calorie-counting. Accessed 28 October 2026.
3. National Institute for Health and Care Excellence, "Overweight and obesity management", NICE guideline NG246, published 14 January 2025, last updated 8 January 2026: recommendations 1.16.1 to 1.16.12 and 1.19.3 to 1.19.6. nice.org.uk/guidance/ng246. Accessed 28 October 2026.
4. Henry CJK. "Basal metabolic rate studies in humans: measurement and development of new equations". Public Health Nutrition 2005;8(7A):1133 to 1152, Tables 12, 14 and 15. doi.org/10.1079/PHN2005801. Accessed 28 October 2026.
5. Leidy HJ and colleagues. "The role of protein in weight loss and maintenance". American Journal of Clinical Nutrition 2015;101(6):1320S to 1329S. Abstract. doi.org/10.3945/ajcn.114.084038. Accessed 28 October 2026.
6. Scientific Advisory Committee on Nutrition (SACN), "Statement on nutrition and older adults living in the community", 20 January 2021, paragraphs 3.2 and 4.22 to 4.24; the 1991 advice on twice the reference intake as restated by the British Nutrition Foundation, "Protein". gov.uk/government/publications/sacn-statement-on-nutrition-and-older-adults. Accessed 28 October 2026.
7. Public Health England, "Government Dietary Recommendations: energy and nutrients for males and females aged 1 to 18 years and 19+ years", 2016, Introduction (page 4) and Table 2 (page 7) with footnotes. assets.publishing.service.gov.uk, government_dietary_recommendations.pdf. Accessed 28 October 2026.
8. Scientific Advisory Committee on Nutrition (SACN), "Carbohydrates and Health", 2015, Summary paragraphs S.15 to S.19, S.22 and S.27. assets.publishing.service.gov.uk, SACN_Carbohydrates_and_Health.pdf. Accessed 28 October 2026.
9. Retained Regulation (EU) No 1169/2011 on the provision of food information to consumers, Annex XIV, Conversion factors. legislation.gov.uk/eur/2011/1169/annex/XIV. Accessed 28 October 2026.
10. World Health Organization, "Total fat intake for the prevention of unhealthy weight gain in adults and children: WHO guideline", 17 July 2023, recommendations 1 and 2 and remarks. who.int/publications/i/item/9789240073654. Accessed 28 October 2026.
11. NHS, "Understanding calories", page last reviewed 17 April 2023. nhs.uk/live-well/healthy-weight/managing-your-weight/understanding-calories. Accessed 28 October 2026.
12. Hall KD and colleagues. "Quantification of the effect of energy imbalance on bodyweight". The Lancet 2011;378(9793):826 to 837. Full text of the author manuscript. pmc.ncbi.nlm.nih.gov/articles/PMC3880593. Accessed 28 October 2026.
13. NHS, "Overweight and obesity in adults", page last reviewed 29 April 2026. nhs.uk/conditions/overweight-and-obesity. Accessed 28 October 2026.

Numbered markers in the page text link to these entries. Statistics describe populations, not any one person’s results.

Published 28 October 2026.