TDEE stands for Total Daily Energy Expenditure: the calories you burn in a typical day, including resting metabolism, activity and the small amount of energy used to digest food. Eat below it to lose weight, at it to hold, above it to gain.

BMR stands for Basal Metabolic Rate: the calories your body burns at complete rest just to keep breathing, circulating blood and producing cells. It's typically 60 to 75 per cent of your total daily burn. Eating below your BMR for long periods isn't recommended.

How accurate is this calculator?

We use the Mifflin-St Jeor equation, published in 1990 and judged the most accurate predictive formula by the American Dietetic Association in 2005. Any equation gives an estimate: genetics, muscle mass, hormones and conditions like thyroid disease all shift the real number. Use the result as a starting point, then adjust based on what the scale actually does over two to three weeks.

kcal The UK calorie calculator

Your daily calorie target, in 30 seconds.

Type your weight, height, age and how active you are. We run the Mifflin-St Jeor equation (the one the dietetic associations rate most accurate) and give you back your BMR, your TDEE, and the targets for losing, holding or gaining.

Sex

The equation uses a different constant for each. Pick the one that matches your body's biology.

Age (years)

Height

Weight

Activity level When you're between two, pick the lower one and adjust after two weeks of real data.

01 How the maths works

The equation,
spelt out.

We use Mifflin-St Jeor (1990). The American Dietetic Association reviewed the common predictive equations in 2005 and judged it the most accurate against indirect calorimetry. Here's what it actually does.

BMR for men

Multiply weight in kilograms by 10, height in centimetres by 6.25, subtract five times your age, add five.

BMR = 10 × kg + 6.25 × cm − 5 × age + 5

BMR for women

Same formula, but subtract 161 at the end instead of adding five. The difference reflects average body composition.

BMR = 10 × kg + 6.25 × cm − 5 × age − 161

From BMR to TDEE

Multiply BMR by an activity factor: 1.2, 1.375, 1.55, 1.725 or 1.9. That covers resting metabolism plus the calories activity and digestion add on top.

TDEE = BMR × activity

From TDEE to a target

Roughly 7,700 kcal per kilogram of body fat. A 500 kcal daily deficit is about half a kilogram a week. Real results depend on adherence, sleep, training and water.

cut = TDEE − 500 · gain = TDEE + 300

02 What happens next in the app

Set the target.
Log against it.

A daily kcal number on its own doesn't change anything. NutraSafe sets your target as a line on the diary and counts every meal, snack and workout against it. Calories go in, protein, carbs, fat, vitamins and additives come with them.

Log meals in a couple of taps.

Search, scan a UK barcode or photograph the plate. Calories and macros fill in automatically.

See the day add up.

A live total against your TDEE target. Cut, hold or gain. Pick your number, the diary does the maths.

iii

Watch the macros, not just the calories.

Protein, carbs and fat tracked alongside, with 14 vitamins and 13 minerals against the UK NRV.

Workouts in the same diary.

Sets, reps, weight, Apple Watch. So the protein and the calories line up with what you actually did.

Get NutraSafe on the App Store → See the food tracker

03 Frequently asked

The questions
that come up.

Everything you'd want to know before trusting a number that came out of an online calculator.

What's the difference between BMR and TDEE?

BMR is what you'd burn if you stayed in bed all day, doing nothing: breathing, blood circulating, cells replacing themselves. TDEE is BMR plus everything else: walking to the kettle, sitting at a desk, training, the small amount used to digest food. Eat below TDEE and you lose weight. Eat above it and you gain.

How accurate is this?

Mifflin-St Jeor (1990) is the equation the American Dietetic Association rated most accurate in its 2005 review of resting metabolic-rate predictors. Any predictive equation gives an estimate, though. Genetics, muscle mass, thyroid health and hormones all shift the real number. Use the result, log against it for two to three weeks, then adjust if the scale isn't moving the way you expected.

Which activity multiplier should I pick?

1.2 if you sit at a desk and barely move. 1.375 for one to three light workouts a week. 1.55 for three to five sessions a week. 1.725 for six to seven hard sessions. 1.9 for twice-a-day training or a heavy manual job. If you sit between two, pick the lower one: people consistently overestimate activity, and a smaller cushion is easier to add back than a too-aggressive cut is to fix.

Can I eat below my BMR to lose faster?

Not advisable. The NHS recommends a maximum 500 to 600 kcal daily deficit for most adults. Long stretches below BMR are associated with muscle loss, hormone disruption and rebound weight gain. If you've a clinical reason for a steeper cut, that's a GP or registered-dietitian conversation, not an online-calculator one.

Why does it use Mifflin-St Jeor and not Harris-Benedict?

Harris-Benedict was published in 1919 and revised in 1984. Mifflin et al. published their equation in 1990 with a sample that better matched the modern adult population, and the predictive accuracy is consistently rated higher in head-to-head reviews. Katch-McArdle is more accurate again if you know your body-fat percentage from a DEXA scan, but most people don't.

Does this account for losing fat without losing muscle?

The calculator gives a calorie target. Body composition (fat vs muscle) is mostly down to protein intake and resistance training. Pro users get the workout side in the same diary, so protein, lifts and calories all sit together.

You've got the number.
Now log against it.

Get NutraSafe on the App Store →

Free download. The food log, the additive flags and 25 entries a day are free. Pro is £3.99 a month or £34.99 a year for unlimited logs, AI Coach, workouts and fasting.

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