Calorie Calculator

How to Use the Calorie Calculator

A calorie target is maintenance plus or minus a percentage. This calculator works out maintenance from your own figures, applies the goal you choose, and — the part most tools omit — tells you what weekly weight change that target actually implies.

1. Enter your height, weight, age and activity level. These produce maintenance calories through the Mifflin-St Jeor equation and an activity multiplier.
2. Pick a goal. Deficits and surpluses are expressed as percentages of maintenance rather than flat numbers, because a 500-calorie deficit is modest for a large athlete and severe for a small sedentary adult.
3. Read the weekly change figure. It converts the daily difference into kilograms and pounds a week using the conventional 7,700 kcal per kilogram, which is the number that makes a target feel real.
4. Check the floor. Targets below roughly 1,500 kcal for men and 1,200 for women are flagged, because sustained intake at that level makes adequate nutrition difficult and muscle loss likely.
5. Compare all six goals in the table. Seeing an aggressive cut and a mild one side by side, with their weekly outcomes, usually settles the choice faster than any advice.

Nothing here accounts for medical conditions, medication, pregnancy or a history of disordered eating. This is arithmetic on population averages, not a plan.

Calorie Target Formula

Maintenance, then a percentage, then a conversion into weight.

Percentage deficits scale with the person, which is why they are preferable to flat numbers. A 20% cut is around 550 kcal for this example and would be roughly 380 kcal for a smaller, less active adult — proportionate in both cases, where a flat 500 would not be.

Example

Maintenance of 2,739.63 kcal, cutting 15%

1. Maintenance: BMR 1,767.50 × 1.55 = 2,739.63 kcal.
2. A 15% cut: 2,739.63 × 0.85 = 2,329 kcal a day.
3. Daily deficit: 2,329 − 2,739.63 = −410.94 kcal.
4. Weekly: 410.94 × 7 = 2,876.58 kcal, divided by 7,700 = 0.374 kg a week.
5. In pounds: 0.374 × 2.20462 = 0.82 lb a week.
6. The target sits well above the 1,500 kcal floor, so there is no warning flag.

How long to lose five kilograms

At a 20% deficit — 2,192 kcal a day, a shortfall of 547.92 — the weekly loss is 0.498 kg, so five kilograms takes about 10 weeks. At the milder 10% deficit it takes just over twenty. Both routes arrive; the slower one is considerably easier to adhere to and loses less muscle along the way, which is why most guidance favours it despite the arithmetic looking worse.

The famous 500-calorie rule

A flat 500 kcal daily deficit gives 3,500 kcal a week, which is 0.4545 kg or almost exactly one pound. That is where the rule of thumb comes from, and it is a reasonable approximation for the first few weeks. It drifts afterwards because maintenance falls as you get smaller, which is why the target needs recalculating every few kilograms.

What a Realistic Rate Looks Like

Every goal, its daily calories and the weight change it implies.

The whole range spans under a kilogram a week. That is the honest picture: meaningful body composition change is measured in months, and any plan promising much more than a kilogram a week is either water, muscle, or not happening.

On the bulking side the arithmetic is less favourable than it looks. A surplus produces weight gain reliably, but the share of that gain which is muscle depends on training, protein intake and how much muscle you already carry — and it is rarely more than half. A larger surplus mostly buys more fat, which is why lean bulking at 10% is the usual recommendation over 20%.

For the cutting side, the constraint that matters most is protein rather than calories. In a deficit the body will take tissue from somewhere, and adequate protein plus resistance training is what steers that towards fat rather than muscle — the protein calculator sets a target and the macro calculator fits it inside your calories.

Five Things This Calculation Does Not Know

Five things this calculation does not know about you.

What you actually eat. Research consistently finds people underreport intake by 20% or more, and the error grows with the size of the meal. A target that is not being hit is far more common than a target that is wrong.

Water weight. Glycogen binds water at roughly three grams per gram stored, so the first week of any deficit shows a drop far larger than fat loss, and the first week of a surplus shows the reverse. Judge nothing from the first ten days.

Adherence. The best diet is the one that gets followed. An aggressive deficit that collapses after three weeks loses less than a mild one sustained for six months, and the arithmetic on this page cannot tell you which you are more likely to keep.

Medical context. Thyroid conditions, diabetes, pregnancy, breastfeeding, several medication classes and any history of disordered eating all change what a sensible target is. None of them are visible to a formula, and all of them are reasons to involve a professional.

Where the weight comes from. The 7,700 kcal per kilogram figure assumes pure fat. Real weight change includes water, glycogen and some lean tissue, so actual results run faster than predicted at first and slower later.

A word on the pace of change, because it is where most plans fail. A deficit of 20% sounds moderate and produces roughly half a kilogram a week at this body size, which is a sensible rate. Doubling that deficit does not double the fat lost; it increases the share of the loss that comes from lean tissue, sharpens hunger, and makes adherence collapse sooner.

The evidence on rate is reasonably consistent: somewhere between 0.5% and 1% of body weight a week preserves muscle well while still producing visible progress. Above that, the returns fall off quickly. A slower plan finished beats a faster plan abandoned in week three, and the calculator cannot tell you which one you will actually complete.

If your weight is not moving as the table says after three or four weeks of consistent intake, the maintenance estimate is wrong rather than the arithmetic. Adjust the target by the difference the scale reports, not by picking a different activity multiplier and hoping.