Macro calculator for weight loss

What a weight-loss macro calculator actually does

It estimates the calories you burn in a day, subtracts a deficit, and splits what is left into grams of protein, fat and carbohydrate. The tool above does the first two steps with the same engine as the TDEE calculator and the macro calculator; this page only re-points the copy at fat loss. Nothing about the arithmetic changes; a weight-loss macro target is a maintenance calculation with one subtraction on the end.

That is worth saying plainly because most calculators present the deficit as the hard part. It is not. The hard part is the maintenance estimate underneath it, which carries a band of roughly ±16%. Subtracting 500 kcal from a number that is itself uncertain by 300 does not give you a precise target: it gives you a starting point you then correct with your own weight data.

Setting the deficit as a percentage, not a flat 500

This calculator applies the deficit as a share of your maintenance calories (usually 10–25%) rather than a flat number. A flat 500 kcal cut is mild for someone maintaining on 3,000 and severe for someone maintaining on 1,700, which is exactly the range of people who use a calculator like this. As a percentage, 15–20% below maintenance lands most people near 0.5–0.7% of bodyweight lost per week, which is the rate the evidence supports for holding on to muscle while the fat comes off.

Bigger deficits do not reliably speed fat loss. They speed weight loss, and a larger share of that faster loss is lean tissue and water. The old "3,500 kcal equals one pound" rule is a useful sketch for a few weeks and drifts after that, because your maintenance falls as you get lighter and your body trims non-exercise movement in response to eating less.

Protein comes first in a deficit

Protein is set from bodyweight, at 1.6–2.2 g per kilogram, and while dieting the upper half of that band is the sensible place to sit. In a calorie deficit adequate protein is the main dietary lever protecting lean mass, and it is also the most filling of the three macros per calorie. Because the target scales with your weight rather than your calorie intake, your protein number barely moves when you cut, which surprises people who expect every macro to shrink together.

The macro calculator page covers where that 1.6–2.2 g/kg range comes from in more detail; a systematic review by Morton and colleagues (2018) found benefits to resistance-training adaptations plateauing at around 1.6 g/kg, with individual data supporting a ceiling closer to 2.2.

Fat and carbs split the rest

After protein, fat is set at 20–30% of the reduced calorie target and carbohydrate takes the remainder. There is a floor on fat worth respecting even when the arithmetic of a deep cut would let you go lower: dietary fat carries the fat-soluble vitamins and supports hormone production. Beyond that floor, the fat-to-carb ratio is mostly preference. If you train hard, leaving more of the remainder as carbohydrate tends to help those sessions; if you prefer eating fewer carbs, nothing breaks.

This is also why a weight-loss split and a maintenance split look so similar. The calorie number changed a lot; the logic did not. Protein anchored to bodyweight, fat a percentage of calories, carbohydrate the flexible remainder, in both directions.

Floors, and when to stop cutting

Below roughly 1,200 kcal for women or 1,500 for men, the tool shows the floor instead of the number the percentage asked for. Those intakes are hard to meet vitamin and mineral needs on, and running them without supervision is not something this page recommends. Very low intake also tends to backfire on adherence: hunger, poor training, low mood and a strong rebound.

A cut is also not meant to run indefinitely. If fat loss stalls for two to three weeks despite honest logging, a short break at maintenance is usually more productive than cutting calories further. The goal is the smallest deficit that still moves the weekly average, held for as long as you can sustain it well.

Replace the estimate with your own data

Once you have a target, the most useful thing you can do is stop trusting it. Eat near it for two to three weeks, weigh yourself each morning under the same conditions, and compare weekly averages rather than individual days: day-to-day swings are water and gut contents. If your average dropped roughly as predicted, the estimate was close. If it barely moved, your real maintenance is lower than the calculator thought; take about 100–150 kcal off and hold for another two weeks.

Two rounds of that beat any equation, because your own weight trend already contains the things no formula can see: your non-exercise movement, your adaptation to eating less, and how accurately you are actually logging. The accuracy page walks through why that is, with the underlying studies.

What this calculator cannot tell you

It cannot see your food quality, your fibre, your micronutrients, your sleep, your training, your stress or your medical history, and weight loss depends on all of them. It also cannot account for conditions that affect metabolism, for medication that changes appetite or energy use, or for a history of disordered eating, where calorie targets can do harm.

This page is written by Madhu Kinnera, who is not a clinician. Nothing here is medical advice. If you are pregnant or breastfeeding, have a condition affecting your metabolism, or are planning a large drop in intake, speak to a doctor or a registered dietitian first.