The NHS puts an average man at 2,500 kcal a day, and most men sit somewhere between 2,200 and 3,200 depending on size and activity. Five methods get you from that population average to a personal number, and they are ranked here by how closely each reflects you: two weeks of tracking, the Mifflin-St Jeor equation, Katch-McArdle, a bodyweight shortcut, and the 2,500 kcal reference itself.
Whatever the calorie target turns out to be, protein is the part of it that decides how much muscle survives a period of weight loss, which is the subject of PhysioHub's guide to how much protein you need.
The five are ranked by how closely each reflects your own requirement. The first measures it, the middle three estimate it from your body, and the last describes an average man who may be nothing like you.
| Method | Best for | What makes it stand out | Accuracy |
|---|---|---|---|
| 1. Two-week track and adjust | Anyone serious about the number | The only method that measures you rather than estimating you | Highest |
| 2. Mifflin-St Jeor plus an activity factor | A solid starting estimate | The best-validated equation for the general population | Good, within about 10 per cent |
| 3. Katch-McArdle | Lean or heavily muscled men | Uses lean mass rather than total weight | Good, if body fat is measured well |
| 4. Bodyweight shortcut | A quick mental estimate | One multiplication, no equation needed | Rough |
| 5. The NHS 2,500 kcal figure | Reading food labels | A population reference everyone already knows | Population level only |
This is a documentary review of published dietary guidance and validated equations rather than a measurement of you. The methods considered were the Mifflin-St Jeor equation, the Harris-Benedict equation and its revisions, the Katch-McArdle formula, the Cunningham equation, the Schofield equations used in UK dietary reference values, bodyweight multipliers, activity trackers, and the track-and-adjust approach.
Three criteria decided the order: how closely the method reflects an individual rather than a population, how much it relies on inputs most people can measure accurately, and how much error it introduces in practice.
The sources read were the NHS guidance on understanding calories, which states that an average man needs 2,500 kcal a day and an average woman 2,000 kcal, and the UK government dietary recommendations derived from the Scientific Advisory Committee on Nutrition's 2011 Dietary Reference Values for Energy, which set the estimated average requirement for men aged 19 to 64 at 10.5 MJ, equal to 2,500 kcal a day. Evidence checked in August 2026.
What could not be checked: no equation has been validated against your own metabolism, and published comparisons find that even the best of them are within about 10 per cent for most people while being substantially wrong for a minority. That is the reason the measured approach ranks first.
Decide what the number is for. Reading food labels needs nothing more than the population figure. Changing body weight deliberately needs a personal estimate, and the more precise the goal, the more the method matters.
Use the inputs you can actually measure. Height and weight are easy to measure accurately, and body fat percentage is not, unless you have a good scan. That is the practical reason Mifflin-St Jeor usually beats Katch-McArdle in real life despite the theory favouring the latter.
Be honest about the activity multiplier. This is where almost all the error enters. Most people select a multiplier one level above their real activity, which produces an estimate 300 to 500 kcal too high before anything has been eaten.
Treat any estimate as a hypothesis. Whatever number you start with, two weeks of consistent eating and regular weighing will tell you whether it was right. That check is worth more than choosing between the equations.
What it is
Recording everything you eat for two weeks while weighing yourself several times a week, then working backwards from the weight change to your actual maintenance intake.
Who it suits
Anyone who wants a number that is genuinely theirs, and anyone whose weight has failed to respond as an equation predicted.
How to do it
Eat as you normally would and log it accurately, using scales rather than estimates for the first week. Weigh yourself each morning after the toilet and before breakfast, then average each week. If weight is stable, your average intake is your maintenance. If it moved by half a kilogram over the fortnight, adjust by roughly 250 kcal a day in the appropriate direction.
What the evidence supports
Every equation on this list estimates the average person with your characteristics, and individual metabolic rates vary around that average by roughly 10 per cent in either direction. Measured intake against measured weight change is the only approach that captures your own value, including the parts no equation contains, such as how much you fidget and how much your daily activity varies.
Limits and cautions
It relies on honest logging, and under-reporting of food intake is well documented and largely unintentional. Weight also fluctuates with hydration, salt and gut contents, which is why weekly averages rather than single readings are used. Anyone with a history of disordered eating should approach detailed tracking cautiously or avoid it.
Time and effort
Around five minutes a day for two weeks, then nothing.
Why it made the list
It ranks first because it is the only method here that measures rather than predicts, and because it corrects whichever equation you started from.
What it is
A validated equation for resting metabolic rate, multiplied by a factor reflecting how active you are.
Who it suits
Almost everyone as a starting point, and the default choice where body fat percentage is unknown.
How to do it
For men, resting rate equals 10 times weight in kilograms, plus 6.25 times height in centimetres, minus 5 times age in years, plus 5. Multiply by 1.2 for sedentary, 1.375 for light activity one to three days a week, 1.55 for moderate activity three to five days, or 1.725 for hard activity six or seven days. A 40-year-old man of 85 kg and 178 cm gets a resting rate of about 1,762 kcal, which becomes roughly 2,430 kcal at a light activity level.
What the evidence supports
Mifflin-St Jeor was developed specifically because the older Harris-Benedict equation overestimated requirements in modern populations, and it has since become the most widely used equation in clinical dietetics for people whose body composition is unknown. It estimates resting metabolic rate within about 10 per cent for the majority of people.
Limits and cautions
The activity multiplier carries most of the error, and it is the input people are least honest about. It also uses total body weight, so it overestimates for someone carrying a lot of fat and underestimates for someone unusually muscular.
Time and effort
Two minutes with a calculator.
Why it made the list
It is the best-validated equation for the general population and it needs only figures you can measure accurately at home.
What it is
An equation based on lean body mass rather than total body weight.
Who it suits
Men who are either very lean or carrying substantially more muscle than average, and anyone who has had a proper body composition scan.
How to do it
Calculate lean mass by multiplying weight by one minus your body fat percentage as a decimal. Resting rate equals 370 plus 21.6 times lean mass in kilograms. Apply the same activity multipliers as above. For an 85 kg man at 15 per cent body fat, lean mass is 72.25 kg, giving a resting rate of about 1,931 kcal.
What the evidence supports
Muscle and organ tissue account for most resting energy expenditure, while fat mass contributes comparatively little. An equation built on lean mass is therefore more accurate in theory, and it does outperform weight-based equations in people at the extremes of body composition, where total weight is a poor proxy for metabolically active tissue.
Limits and cautions
It is only as good as the body fat measurement, and consumer body fat scales are frequently wrong by five to ten percentage points, which introduces more error than it removes. Without a DEXA or a skilled skinfold measurement, this is usually less accurate in practice than Mifflin-St Jeor.
Time and effort
Two minutes, plus whatever the body composition measurement takes.
Why it made the list
For the specific group of people whose body composition is far from average and accurately known, it is the better equation. For everyone else the extra input adds error rather than removing it.
What it is
Multiplying body weight in kilograms by a single number to get daily calories.
Who it suits
Anyone wanting a workable estimate in ten seconds without an equation.
How to do it
Multiply weight in kilograms by 26 to 28 for a sedentary man, 30 to 33 for someone moderately active, and 35 to 38 for someone training hard most days. An 85 kg moderately active man lands around 2,550 to 2,800 kcal.
What the evidence supports
The shortcut approximates the output of the full equations for people of average height and age, because body weight is the largest single driver of energy requirement. Its accuracy falls away for anyone unusually tall or short, and for older adults, because it ignores both height and age entirely.
Limits and cautions
It uses total body weight, so it overestimates substantially for anyone carrying a large amount of fat, which is the group most likely to be using it to plan weight loss. It is best treated as a first guess to be corrected by measurement.
Time and effort
Ten seconds.
Why it made the list
It is close enough to be useful for a starting point, and its simplicity means people actually use it rather than abandoning the exercise.
What it is
The population reference used on food labels and in public health guidance for an average man.
Who it suits
Everyone, for reading food packaging and getting a sense of scale.
How to do it
Use it as a yardstick rather than a target. The NHS states that an average man needs 2,500 kcal a day and an average woman 2,000 kcal, adding that individual figures differ with age, weight, height and exercise.
What the evidence supports
The figure comes from the Scientific Advisory Committee on Nutrition's 2011 Dietary Reference Values for Energy, which set the estimated average requirement for men aged 19 to 64 at 10.5 MJ a day, equal to 2,500 kcal. An estimated average requirement is by definition the midpoint of a population, so around half of men need more than it and half need less.
Limits and cautions
Used as a personal target it will be wrong for most individuals, and the direction of the error is unpredictable. A 60 kg sedentary man and a 100 kg man training five times a week can differ by more than 1,200 kcal a day, and the same single figure describes them both.
Time and effort
None.
Why it made the list
It is the number everyone has already met, and understanding what it actually represents is what stops it being used as a personal prescription.
| Method | Inputs needed | Main source of error | Time to get a number | Best used for |
|---|---|---|---|---|
| Two-week track and adjust | Food logs, regular weights | Under-reporting of intake | Two weeks | A number that is genuinely yours |
| Mifflin-St Jeor | Weight, height, age, activity | The activity multiplier | Two minutes | The default starting estimate |
| Katch-McArdle | Weight, body fat percentage, activity | Inaccurate body fat readings | Two minutes | Very lean or very muscular men |
| Bodyweight shortcut | Weight, activity level | Ignores height and age | Ten seconds | A quick first guess |
| NHS 2,500 kcal figure | None | Describes an average, not you | None | Reading food labels |
The second column explains the ranking. The methods that need the fewest inputs are the ones that describe you least, and the one that needs the most effort is the only one that measures anything.
If you just want to make sense of food labels, the 2,500 kcal figure is exactly what it was designed for.
If you want to change your weight deliberately, start with Mifflin-St Jeor, then run the two-week check and adjust from what actually happened.
If you are lean and training hard, use Katch-McArdle if you have a real body composition measurement, and Mifflin-St Jeor if your only reading came from a bathroom scale.
If you are losing weight quickly, recalculate every 5 kg, because the requirement falls as body weight falls, and add strength training so the loss comes from fat rather than muscle. Our guide to exercise for abdominal fat loss covers the training side.
If you only change one thing inside the number, make it protein. Our guide to how much protein you need sets out the amounts that matter.
The assumption that arrives with this topic is that the calorie number is the hard part, and that getting it right is what decides the outcome. In practice the number is usually close enough on the first attempt, and what goes wrong sits elsewhere.
The pattern seen most often in clinic is a man who has set a sensible deficit, lost weight steadily for two months, and arrived with a knee or a back that has started complaining. What has happened is that the weight came off without any resistance training alongside it, so a meaningful share of it was muscle, and the muscle lost is what a knee relies on for stairs and a back relies on for lifting. The calorie target was fine. The missing piece was the two strength sessions a week and enough protein to make them count, which together change what is left at the end of the process rather than how fast it happens.
Where the aim is to lose weight while getting stronger rather than weaker, our 1:1 rehab and strength training sessions are built around that combination.
How many calories should a man eat a day?
The NHS uses 2,500 kcal a day as the figure for an average man, alongside 2,000 kcal for an average woman, and states plainly that individual needs vary with age, weight, height and activity. Most men fall somewhere between 2,200 and 3,200 kcal a day depending mainly on body size and how active they are, which is why a personal estimate is more useful than the population average.
What is the most accurate way to work out my calories?
Tracking what you actually eat for two weeks while weighing yourself regularly, then adjusting. Every equation estimates an average person of your size, and measured intake against measured weight change tells you about you. Equations are the starting point and the two-week check is the correction.
How many calories to lose weight as a man?
A deficit of 500 kcal a day below maintenance produces roughly half a kilogram of weight loss a week for most men, which is a rate that is generally sustainable and preserves muscle reasonably well. Deficits larger than about 1,000 kcal a day tend to cost more muscle and are harder to maintain.
Do older men need fewer calories?
Somewhat, and less than commonly assumed. Resting metabolic rate falls gradually with age, largely because muscle mass falls, and most of the drop in daily needs comes from reduced activity rather than from age itself. Strength training slows both, which is one reason it matters more with each decade.
Is 1,500 calories a day too low for a man?
For most men, yes, as a sustained intake. It sits well below the estimated requirement for an average man and makes it difficult to obtain enough protein and micronutrients. Very low calorie diets have a place under medical supervision, and they are a supervised intervention rather than a default.
Does exercise mean I can eat much more?
Less than most people assume. An hour of brisk walking burns around 300 kcal for an average man and an hour of running around 700. Fitness trackers commonly overestimate this by 20 to 90 per cent depending on the activity, so treating the tracker's number as a licence to eat is one of the most common reasons a deficit fails to produce weight loss.
How much protein should I eat within those calories?
For general health the UK reference intake is around 0.75 g per kilogram of body weight a day, and for anyone training regularly or losing weight the evidence supports considerably more, in the range of 1.6 to 2.2 g per kilogram. That is usually the single most useful thing to get right inside a calorie target.
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