How Many Calories Should You Eat? BMR, TDEE, and a Real Example
The number of calories you should eat starts with two figures: your BMR, the calories your body burns at rest, and your TDEE, that same number scaled up for how active you actually are. A 30-year-old man at 180 cm and 80 kg with a moderately active lifestyle burns about 2,759 kcal a day just maintaining his current weight. Eating above or below that number is what moves the scale.
What BMR and TDEE actually mean
BMR (calories at rest) is the energy your body needs just to keep running: breathing, circulating blood, keeping your organs and brain going, even if you never left your bed. It’s not a hypothetical, it’s the baseline every other number in this article builds on.
TDEE (maintenance calories) takes that baseline and multiplies it by an activity factor, everything from a desk job with no exercise to daily hard training. TDEE is the calorie number that keeps your weight stable. Eat less than TDEE and you lose weight over time, eat more and you gain it. The most common formula for BMR, and the one used here, is Mifflin-St Jeor: for men it’s 10 times weight in kg, plus 6.25 times height in cm, minus 5 times age, plus 5. For women, swap that final +5 for -161.
Worked example: 180 cm, 80 kg, 30-year-old man
Here’s the full calculation for a moderately active man who is 180 cm tall (about 5’11”) and weighs 80 kg (about 176 lbs).
| Step | Calculation | Result |
|---|---|---|
| BMR | 10 × 80 + 6.25 × 180 − 5 × 30 + 5 | 1,780 kcal/day |
| TDEE (moderate activity, ×1.55) | 1,780 × 1.55 | 2,759 kcal/day |
Once you have TDEE, every calorie target is just an offset from it:
| Goal | Formula | Calories/day |
|---|---|---|
| Gain | TDEE + 500 | 3,259 |
| Mild gain | TDEE + 250 | 3,009 |
| Maintain | TDEE | 2,759 |
| Mild loss | TDEE − 250 | 2,509 |
| Loss | TDEE − 500 | 2,259 |
Nothing here is guesswork. Pick a goal, apply the matching offset to your own TDEE, and that’s your daily target.
Does activity level change everything?
It changes more than most people expect, and it’s the single biggest lever in the whole equation, bigger than the difference between two people of similar size. Take that same 180 cm, 80 kg, 30-year-old man and run his BMR of 1,780 kcal through each activity multiplier instead of just one.
| Activity level | Multiplier | TDEE |
|---|---|---|
| Sedentary (little or no exercise) | 1.2 | 2,136 |
| Light (exercise 1-3 days/week) | 1.375 | 2,448 |
| Moderate (exercise 3-5 days/week) | 1.55 | 2,759 |
| Active (exercise 6-7 days/week) | 1.725 | 3,071 |
| Very active (hard daily training) | 1.9 | 3,382 |
That’s a swing of 1,246 kcal a day, roughly 8,700 kcal a week, between the least and most active version of the exact same body. Two people with identical height, weight, and age can have completely different calorie needs depending on how they actually move through their week. This is also why being honest about your activity level matters more than getting the BMR formula exactly right: overestimate how active you are and every target downstream is inflated.
Men vs. women: why the formula differs
The Mifflin-St Jeor equation uses the same base for both sexes (10 × weight in kg plus 6.25 × height in cm minus 5 × age), then adds a fixed adjustment: +5 for men, -161 for women. That 166-point gap reflects average differences in body composition, men typically carry more muscle mass relative to body weight, and muscle burns more energy at rest than fat does. It’s a population average, not a rule for any one individual, though it’s accurate enough to be the standard formula in clinical and fitness settings today.
Take a 30-year-old woman, 165 cm tall, 65 kg, also moderately active:
BMR = 10 × 65 + 6.25 × 165 − 5 × 30 − 161 = 650 + 1,031.25 − 150 − 161 = 1,370 kcal/day
TDEE = 1,370 × 1.55 = 2,125 kcal/day
Compare that to the male example above (TDEE of 2,759 at the same activity level) and the gap is 634 kcal a day, driven by the combination of the sex adjustment plus the smaller height and weight in this particular example. Run your own numbers through the calculator below rather than assuming either example applies to you.
Get your own BMR and TDEE
Enter your height, weight, age, sex, and activity level, and get your BMR, TDEE, and calorie target for every goal, calculated right in your browser.
How long will it actually take?
This is the part most calorie articles skip: once you know your deficit, you can work out roughly how long a weight loss goal will take. One kilogram of body fat holds approximately 7,700 kcal, so a daily deficit divides directly into a timeline. Here’s how long it takes to lose 5 kg at three different deficit sizes.
| Daily deficit | Days to lose 5 kg | Roughly |
|---|---|---|
| 250 kcal/day | 38,500 / 250 = 154 days | ≈ 22 weeks |
| 500 kcal/day | 38,500 / 500 = 77 days | ≈ 11 weeks |
| 750 kcal/day | 38,500 / 750 ≈ 51 days | ≈ 7.3 weeks |
Doubling the deficit roughly halves the timeline, which makes a bigger deficit tempting. But a 750 kcal/day cut is much harder to sustain for weeks at a time, and steep deficits are more likely to eat into muscle mass along with fat, not just fat. A moderate deficit that you can actually stick to for the full timeline usually beats a faster one you abandon after two weeks.
Common mistakes and limitations
Treating TDEE as an exact number. TDEE from any formula, including Mifflin-St Jeor, is a population-average estimate, not a lab measurement of your individual metabolism. It gets you a solid starting point, not a guarantee.
Not adjusting after a few weeks. Your TDEE isn’t fixed. As you lose or gain weight, your BMR shifts too, since it’s partly a function of your current body weight. Track your progress for two to three weeks, and if the scale isn’t moving the way your calorie target predicted, recalculate and adjust rather than assuming the original number is still correct.
Ignoring muscle mass. The formula only takes in height, weight, age, and sex, it has no way to know if you’re carrying unusually high or low muscle mass for your size. Someone very muscular will typically burn more than the formula predicts, and someone with very low muscle mass will typically burn less.
Applying adult formulas to teenagers. Mifflin-St Jeor was developed and validated on adults. Teenagers are still growing, and their energy needs are driven by growth patterns that an adult formula doesn’t account for. Pediatric guidance, not a generic calorie calculator, is the right source for anyone still in adolescence.
Guessing activity level too generously. As the table above shows, activity level alone can swing TDEE by over 1,200 kcal a day. Most people overestimate how active they are; if you’re unsure, it’s usually safer to round down to the more conservative multiplier.
None of this is medical advice. These formulas are useful estimates for healthy adults, and anyone starting a new diet or training plan, especially with an existing health condition, should check in with a doctor or registered dietitian first.
Frequently asked questions
What’s the difference between BMR and TDEE? BMR is the calories your body burns at complete rest, just keeping your organs and systems running. TDEE takes that number and multiplies it by an activity factor to account for exercise and daily movement, giving you the total calories you burn, and therefore need to eat, to maintain your current weight.
How many calories should I eat to lose weight? Start from your TDEE and subtract 250 to 500 kcal a day. A 250 kcal deficit is a mild, easier to sustain cut, while 500 kcal produces faster results but is harder to maintain and carries more risk of muscle loss. Using the male example above, that means eating around 2,509 kcal (mild loss) or 2,259 kcal (loss) instead of the 2,759 kcal maintenance level.
Why do men and women have different calorie needs at the same weight? The Mifflin-St Jeor formula applies a fixed adjustment, +5 for men and -161 for women, reflecting average differences in muscle mass between the sexes. More muscle burns more calories at rest, so at an identical height, weight, and age, the formula gives men a somewhat higher BMR on average.
Is the Mifflin-St Jeor formula accurate for everyone? It’s the most accurate formula in general use today, but it’s still a population average built from group data, not a direct measurement of your metabolism. It works well as a starting estimate for most healthy adults, but individual metabolic rate can vary from the formula’s prediction, which is why checking progress after a few weeks and adjusting matters more than the formula being perfectly precise.
How often should I recalculate my calorie needs? Recalculate whenever your weight changes meaningfully, roughly every 5 kg (about 10 lbs), or every four to six weeks during an active diet or bulk. Your BMR shifts as your body weight changes, so a target calculated at the start of a diet gradually becomes less accurate the more weight you lose or gain.
Can I use these numbers if I’m pregnant or breastfeeding? No. Pregnancy and breastfeeding both increase calorie needs beyond what a standard TDEE formula accounts for, and the right target depends on individual medical factors. Talk to a doctor or a registered dietitian for calorie guidance during pregnancy or while breastfeeding rather than relying on a general calculator.