How many calories do you need? BMR and TDEE explained

By Zulu Calculator · Updated 19 October 2026 · Health

The calories you need a day to keep your weight steady are your TDEE (total daily energy expenditure). The usual way to estimate it is to work out your resting burn, your BMR, from your weight, height, age and sex, then multiply it by an activity factor between 1.2 and 1.9. For a 30-year-old woman who is 165 cm tall and weighs 65 kg, with light exercise 1 to 3 days a week, that gives a BMR of 1,370 kcal and a TDEE of about 1,884 kcal a day.

This guide explains what BMR and TDEE are, the published equations our calculators use, how much the activity level matters, why any estimate can be 10% or more out, and how a gentle deficit or surplus is worked out. To get your own numbers, use the TDEE calculator.

This is general information, not medical advice. The calculators are for adults aged 18 to 100 and are not suitable for pregnancy, breastfeeding, under-18s or medical decisions. If you are in any of those groups, have a medical condition or a history of eating disorders, or plan big changes to how you eat, talk to a doctor or registered dietitian first.

What is the difference between BMR and TDEE?

BMR (basal metabolic rate) is the energy your body uses in a day lying completely still: breathing, pumping blood, keeping warm and running your brain, liver and kidneys. It is usually the biggest part of what you burn. RMR (resting metabolic rate) is measured more loosely and usually comes out a little higher, but the two words are often used for the same thing.

TDEE is everything you burn in 24 hours. It has four parts:

• BMR, your resting burn.
• NEAT (non-exercise activity thermogenesis): everyday moving such as walking, standing, housework and fidgeting. It varies a lot between people and is often bigger than exercise.
• Exercise: planned workouts and sport.
• TEF (thermic effect of food): the energy used to digest what you eat, about 10% of your intake on a mixed diet. Protein takes more energy to digest than carbs or fat.

Eat about your TDEE and your weight stays roughly the same, which is why it is also called maintenance calories. For the example woman, BMR is 1,370.25 ÷ 1,884.09 = about 73% of her TDEE.

Which equations do the calculators use?

All three of our calculators start from the published Mifflin–St Jeor (1990) equation, the usual default for adults. In Advanced mode you can switch to other published equations. W is weight in kg, H is height in cm, A is age in years, and lean mass is weight × (1 − body fat %).

Mifflin–St Jeor BMR = 10 × W + 6.25 × H − 5 × A, then + 5 for men or − 161 for women
TDEE = BMR × activity factor
Katch–McArdle BMR = 370 + 21.6 × lean mass in kg

• Harris–Benedict, the classic equation from 1919, revised by Roza and Shizgal in 1984 (women 447.593 + 9.247W + 3.098H − 4.330A; men 88.362 + 13.397W + 4.799H − 5.677A). It tends to read a little higher.
• Katch–McArdle and Cunningham (1980) (500 + 22 × lean mass) work from lean mass, so they suit people who know their body fat from a reliable test such as a DEXA scan. Cunningham reads higher and is popular with athletes.
• WHO/FAO/UNU (1985) uses only weight, sex and age band (from Schofield's data), so it is handy when height is not known.

The calorie calculator offers Mifflin–St Jeor, revised Harris–Benedict and Katch–McArdle; the BMR and TDEE calculators offer six, including the original Harris–Benedict. Equations often differ by 50 to 150 kcal a day for the same person.

What are the activity multipliers?

All three calculators use the same five factors. The examples are the plain descriptions from the TDEE calculator.

TDEE at each activity level for a 30-year-old woman, 165 cm, 65 kg (BMR 1,370.25 kcal)

The gap between the lowest and highest level is 2,603 − 1,644 = 959 kcal a day for the same person, much more than the 71 kcal spread between the four equations that work without body fat (1,370.25 to 1,441.63 kcal). So choose your activity level carefully. Most people overestimate how active they are. If you are unsure between two levels, pick the lower one.

Can I work out TDEE from my steps instead?

Yes. The TDEE calculator's Advanced mode can build TDEE from parts instead of a single factor, using rough rules of thumb:

TDEE = (BMR + steps × 0.0005 × W + exercise a day) ÷ (1 − TEF share)
exercise a day = sessions a week × hours a session × (MET − 1) × W ÷ 7

Steps count about 0.0005 kcal per kg of body weight per step, or about 35 kcal per 1,000 steps at 70 kg. MET values come from the Compendium of Physical Activities (2011); only the energy above rest (MET − 1) is counted, because BMR already covers the resting part.

For the same woman with 7,000 steps a day and three 45-minute weight sessions a week (MET 3.5): steps 7,000 × 0.0005 × 65 = 227.5 kcal; one session 0.75 × (3.5 − 1) × 65 = 121.875 kcal, so 3 × 121.875 ÷ 7 = 52.23 kcal a day on average. TDEE = (1,370.25 + 227.5 + 52.23) ÷ 0.9 = 1,649.98 ÷ 0.9 = 1,833.31 kcal. The calculator also shows training-day and rest-day figures.

Why can the estimate be 10% or more out?

Every equation is fitted to measurements from groups of people, so it gives a typical figure for someone of your size, age and sex, not your own. Real energy use can differ by 10% or more because of muscle mass, genetics, hormones, illness and medicines. The calorie calculator puts the range for individual needs at up to 10–20%.

For the example woman, 10% either side of 1,884.09 kcal is about 1,696 to 2,073 kcal a day.

The best check is your own weight. Eat close to your estimated TDEE for two or three weeks and track your average weight. If it stays steady, that is your maintenance. If it creeps up or down, adjust by 100 to 200 kcal.

How many calories should I eat to lose or gain weight?

The calculators use the usual rule of thumb that a kilogram of body weight is about 7,700 kcal (a pound is about 3,500).

daily change = kg a week × 7,700 ÷ 7
0.25 kg a week ≈ 275 kcal a day; 0.5 kg a week ≈ 550 kcal a day

So eating about 250 to 500 kcal less than you use each day leads to a gradual loss of roughly 0.25 to 0.5 kg (0.5 to 1 lb) a week, and the same amount above TDEE leads to a gradual gain. Up to 1 kg (2 lb) a week is possible but harder to keep up, and the calorie calculator marks that pace as fast. The calorie calculator also notes that the NHS suggests 0.5 to 1 kg a week as a safe pace.

Progress slows over time, because a lighter body uses less energy and the same intake leaves a smaller gap. Recheck your numbers every few kilos.

Is there a lowest number of calories the calculators will suggest?

Yes, and the two tools use different safety limits:

• Calorie calculator: never goes below 1,200 kcal a day for women or 1,500 kcal for men, because very low intakes make it hard to get the nutrients you need without medical supervision. When a target hits that floor, the plan simply takes longer. If your goal weight is below a BMI of 18.5 (see BMI explained), it asks you to talk to a doctor before aiming for it.
• TDEE calculator: its rough targets never go below your BMR or the same 1,200 / 1,500 kcal minimum, whichever is higher. A row held there (marked *) means that pace may not suit you. If your maintenance calories are already at or below that level, the loss rows say Not suggested instead of a number. It only shows gentle rows, nothing faster than 0.5 kg a week.

Worked examples

Example 1: 30-year-old woman, 165 cm, 65 kg, light exercise

• BMR (Mifflin–St Jeor): 10 × 65 + 6.25 × 165 − 5 × 30 − 161 = 650 + 1,031.25 − 150 − 161 = 1,370.25 kcal
• TDEE: 1,370.25 × 1.375 = 1,884.09 kcal a day, or 1,884.09 × 7 = 13,188.66 kcal a week. In kJ, 1,884.09 × 4.184 = about 7,883 kJ.
• Lose about 0.25 kg a week: 1,884.09 − 275 = 1,609.09, shown as 1,610 kcal.
• Lose about 0.5 kg a week: 1,884.09 − 550 = 1,334.09 kcal. The calorie calculator shows 1,330 kcal, which is above her 1,200 floor. The TDEE calculator holds this row at her BMR, shown as 1,370 kcal, because 1,334 is below it, and marks it as a pace that may not suit her.
• Gain about 0.25 kg a week: 1,884.09 + 275 = 2,159.09, shown as 2,160 kcal.

Example 2: 40-year-old man, 180 cm, 85 kg, 18% body fat, moderate exercise

• BMR (Mifflin–St Jeor): 10 × 85 + 6.25 × 180 − 5 × 40 + 5 = 850 + 1,125 − 200 + 5 = 1,780 kcal
• TDEE: 1,780 × 1.55 = 2,759 kcal a day
• With his body fat: lean mass 85 × (1 − 0.18) = 69.7 kg. Katch–McArdle BMR = 370 + 21.6 × 69.7 = 370 + 1,505.52 = 1,875.52 kcal, so TDEE = 1,875.52 × 1.55 = 2,907.06 kcal, about 148 kcal more.
• Across all six equations his BMR runs from 1,780 kcal (Mifflin–St Jeor) to 2,033.4 kcal (Cunningham: 500 + 22 × 69.7), a spread of about 253 kcal.
• Lose about 0.5 kg a week on Mifflin–St Jeor: 2,759 − 550 = 2,209, shown as 2,210 kcal, well above both his BMR and the 1,500 kcal floor.

Example 3: 55-year-old woman, 157 cm, 58 kg, little or no exercise, aiming for 54 kg

• BMR (Mifflin–St Jeor): 10 × 58 + 6.25 × 157 − 5 × 55 − 161 = 580 + 981.25 − 275 − 161 = 1,125.25 kcal
• TDEE: 1,125.25 × 1.2 = 1,350.30 kcal a day
• A 550 kcal gap for 0.5 kg a week would mean about 800 kcal a day, and even a 275 kcal gap would mean about 1,075 kcal. Both are below her BMR and below the 1,200 kcal a day that both calculators treat as the usual minimum for women, so neither calculator suggests them. Both hold every loss row at 1,200 kcal instead.
• 1,200 kcal is the lowest figure the calculators will show, not a target to aim for. It leaves a gap of only 1,350.30 − 1,200 = 150.30 kcal a day, so losing 4 kg would take about 4 × 7,700 ÷ (150.30 × 7) = 30,800 ÷ 1,052.10 = 29 weeks, instead of 8 weeks at 0.5 kg a week.
• At 54 kg her needs drop to (540 + 981.25 − 275 − 161) × 1.2 = 1,085.25 × 1.2 = about 1,302 kcal a day.

When needs are this low, cutting further is not the answer. A slower pace is fine, and moving more raises TDEE: at the light activity level her TDEE would be 1,125.25 × 1.375 = about 1,547 kcal a day. If you are in a similar position, a doctor or registered dietitian can help you find a safe plan.

Common mistakes

• Treating BMR as a diet target. BMR is only your burn lying still. Most people need noticeably more.
• Picking too high an activity level. This can move the result by hundreds of kcal a day. If unsure, pick the lower level.
• Counting exercise twice. If you use an activity factor, your workouts are already in it.
• Using Katch–McArdle with a guessed body fat. The lean-mass equations suit people who know their body fat from a reliable test, such as a DEXA scan.

What to do with your number

1. Get your estimate from the TDEE calculator, choosing your activity level honestly.
2. Test it against your average weight over two or three weeks, and adjust by 100 to 200 kcal if it drifts.
3. Plan a goal, if you have one, with the calorie calculator, which gives a target, a timeline and the calories to keep your new weight. The macro calculator splits it into protein, carbs and fat.

Quick summary

• BMR is your burn at complete rest; TDEE is everything you burn in a day.
• TDEE = BMR × activity factor, from 1.2 to 1.9.
• Any estimate can be 10% or more out. Check it against your weight.
• About 275 kcal a day changes weight by about 0.25 kg a week; 550 kcal by about 0.5 kg.
• The calorie and TDEE calculators never go below 1,200 kcal (women) or 1,500 kcal (men), and the TDEE calculator never goes below your BMR either.

For your resting burn on its own by six equations, see the BMR calculator. To find your body fat for the lean-mass equations, try the body fat calculator.

Equations, activity factors and safety limits as used by our TDEE, BMR and calorie calculators: the published Mifflin–St Jeor (1990), Harris–Benedict (1919 and the 1984 revision), Katch–McArdle, Cunningham (1980) and WHO/FAO/UNU (1985) equations, and MET values from the Compendium of Physical Activities (2011). Figures worked out on 19 October 2026.

This guide explains the rules in plain English for planning. It is not legal, financial or flight-operations advice; check your contract, the official source linked above, your employer or your operator.