How many calories should I eat to lose weight? (with the math)

The honest answer is a range, not a single number, because it depends on your size, age, sex, and how active you are. But the math behind that range is simple and you can do it yourself in a few minutes.

This post walks through the same three steps a calorie calculator runs behind the scenes: find your resting energy use, scale it up for activity, then subtract a deficit sized to your goal. We will use a worked example with real numbers so you can follow along with your own.

Step 1: find your BMR with Mifflin St Jeor

BMR stands for basal metabolic rate, roughly the energy your body burns at rest just to keep running. The Mifflin St Jeor equation is a well established way to estimate it from weight, height, age, and sex.

• Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
• Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161

Plug in your own numbers and you get a daily calorie figure. This is not what you eat, it is what your body would burn lying still all day.

Two people at the same weight and height can still land on different BMR numbers because age and sex change the equation. That is expected. The formula is an estimate built from population averages, not a measurement of your exact metabolism, so treat the output as a solid starting point rather than a fixed truth.

Step 2: turn BMR into TDEE with an activity multiplier

BMR alone ignores movement, so the next step multiplies it by an activity factor to get TDEE, your total daily energy expenditure. This is the number you would need to eat to hold your weight steady.

Pick the row that honestly matches your week, not the one you wish matched it. Overestimating activity is one of the most common reasons the math stops working.

Think about a typical week, not your best one. If you train three days and sit at a desk the other four, moderate is usually the honest pick, even if a couple of those training sessions felt intense. The multiplier is meant to reflect your average week over a month, not the single hardest day in it.

Step 3: a full worked example

Say we have a woman, 34 years old, 68 kg, 165 cm tall, who trains 3 to 5 days a week.

BMR = 10 × 68 + 6.25 × 165 − 5 × 34 − 161 BMR = 680 + 1031.25 − 170 − 161 BMR ≈ 1380 kcal per day

Now apply each multiplier so you can see how much activity level changes the target:

She trains moderately, so her TDEE is about 2139 kcal per day. That is the number she would eat to maintain her current weight.

Step 4: set the deficit for your goal

To lose weight, you eat below TDEE. About 7700 kcal equals roughly 1 kg of body fat, so a 500 kcal daily deficit works out to about 0.5 kg per week.

Continuing the example: 2139 − 500 = 1639 kcal per day as her target. Over a week that is a deficit of about 3500 kcal, close to the 3850 kcal in a kilogram of fat, which lines up with losing roughly 0.5 kg a week.

It helps to check that pace against body weight too. Safe fat loss is generally about 0.5 to 1 percent of body weight per week. For someone at 68 kg, that is roughly 0.34 to 0.68 kg per week, so a 500 kcal deficit sits right inside the safe range for her.

If your own numbers put you well outside that range, the deficit is too aggressive or too small for your weight, and it is worth adjusting rather than pushing through. You can run your own numbers through the free calorie calculator instead of doing this by hand every time, and get the same result faster.

Common mistakes that stall the math

A few things quietly break this calculation for most people:

• Guessing activity level too high. A desk job with two gym sessions a week is closer to light than very active.
• Not updating the numbers as weight changes. BMR drops as body weight drops, so a target set at the start needs revisiting every several weeks.
• Underreporting intake. Studies consistently show people underestimate how much they eat when self reporting, which quietly erases the deficit on paper even when the plan looks right.
• Ignoring protein. A deficit without enough protein makes it harder to hold onto muscle. Our protein per kg guide covers how much to aim for during a cut.

None of these mean the math is wrong. They mean the inputs drifted, and the fix is checking them again rather than abandoning the approach.

It also helps to look at trends over two to three weeks rather than any single day. Water weight, sodium, and hormonal shifts move the scale daily in ways that have nothing to do with fat loss. The deficit is doing its job even on a week when the number on the scale barely moves, as long as the average trend over several weeks is heading down.

Why the tracking method matters here

This entire calculation assumes your logged intake matches what you actually eat. If logging a meal takes two or three minutes of searching and scrolling, it is easy to skip the small stuff, and the deficit on paper stops matching the deficit in real life.

Logma logs a meal from a spoken sentence in about 3 seconds, portions estimated from how you describe them, so the habit is easier to keep through a whole cut. For more on how the deficit itself works over time, see our full breakdown of calorie deficit explained.

FAQ

Is Mifflin St Jeor accurate for everyone?

It is a well established estimate, not a lab measurement, so treat the result as a starting point. Adjust it up or down every few weeks based on how your actual weight trend responds.

What if I do not know my activity level exactly?

Pick the multiplier that matches a typical week, not your best week. Most people are closer to light or moderate than they expect.

How fast should I expect to lose weight safely?

A common guideline is about 0.5 to 1 percent of body weight per week. Faster than that for long stretches raises the risk of losing muscle along with fat.

Do I need to recalculate my target as I lose weight?

Yes. BMR falls as body weight falls, so a target set at 80 kg will be too high once you reach 70 kg. Recalculate every several weeks or whenever progress stalls.