a calorie deficit means eating 15–20% less than you burn. Work out your total daily energy expenditure (TDEE), subtract 15–20%, and that's your target intake for fat loss.Example: if you burn 2,200 kcal a day, a 15% deficit is about 330 kcal — roughly 1,870 kcal per day.
"Eat less, move more" is solid advice that's useless without numbers. Cut too little and nothing visibly changes; cut too much and your energy, sleep, and muscle pay the price. This guide walks through the math step by step: how much energy you burn, how much to eat to lose fat, and how to check your numbers against reality. All you need is your weight, height, age, and a calculator.
01. What a calorie deficit actually is
Your body burns energy around the clock: powering your brain, heart, and lungs, digesting food, taking steps, getting through workouts. When food delivers less energy than you spend, your body covers the gap from its reserves — mostly body fat. That's the whole idea of a calorie deficit: not a special diet or a list of banned foods, just the difference between energy in and energy out.
Two practical takeaways follow. First, you can lose weight on any foods as long as the weekly balance is negative — although vegetables, whole grains, and protein keep you full longer, so sticking to the plan gets easier. Second, no single food or supplement "burns fat" on its own. Only the overall balance matters, which means the whole task comes down to two numbers: what you burn and what you eat.
02. Step 1: calculate your basal metabolic rate
BMR is the energy your body burns at complete rest — keeping your organs running and your temperature stable. The Mifflin-St Jeor equation gives the most accurate estimate for most people:
- men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5;
- women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161.
Example: a woman, 70 kg, 165 cm tall, 30 years old. BMR = 700 + 1,031 − 150 − 161 ≈ 1,420 kcal. That's what her body burns even if she spends the entire day on the couch with a book.
03. Step 2: factor in your activity
BMR is the floor. Your real daily burn (TDEE) is higher: steps, chores, and workouts all add up. Multiply your BMR by an activity factor:
| Lifestyle | Multiplier |
|---|---|
| Desk job, barely any movement | 1.2 |
| 1–3 light workouts a week | 1.375 |
| 3–5 workouts a week | 1.55 |
| Hard training 6–7 days a week | 1.725 |
Our example trains three times a week and walks a lot: 1,420 × 1.55 ≈ 2,200 kcal — that's her daily expenditure.
almost everyone overestimates their activity. If you're torn between two multipliers, pick the lower one — better to underestimate your burn now than spend a month wondering why the scale won't move.
04. Step 3: choose your deficit size
The working range is 15–20% of TDEE. That pace typically means losing about 0.5–1% of body weight per week: fat comes off while you keep the energy to train and live your life. In our example: 2,200 × 0.15 ≈ 330 kcal, so the target is around 1,870 kcal a day.
Cutting harder is tempting, but deficits above 25% usually end in binges, constant fatigue, and muscle loss — which lowers your energy expenditure and makes fat loss even harder. One more guardrail: don't eat below your BMR. If the math pushes you under it, shrink the deficit and add movement instead — an extra 2,000–3,000 steps a day works well.
05. Step 4: test and adjust
Every formula carries a 10–15% margin of error, so reality makes the final call. Weigh yourself every morning under the same conditions and compare weekly averages, not individual days: water weight swings by 1–2 kg and easily hides real progress.
After two to three weeks, look at the trend:
- losing 0.5–1% of body weight per week — the math checks out, change nothing;
- the scale isn't moving — cut another 100–150 kcal or add 2,000–3,000 steps;
- losing faster than 1.5% per week — add 100–150 kcal back: rushing costs muscle and disrupts hormones.
Recalculate your TDEE every 4–6 weeks: as your weight drops, so does your burn, and the old deficit slowly evaporates.
The bottom line
Calculating a deficit takes five minutes: BMR from the formula, multiply by an activity factor, subtract 15–20%. From there, consistency does the real work: a month in a moderate deficit beats a week of heroic starvation followed by a rebound. Track honestly, weigh yourself regularly, judge by weekly averages — and the weight comes off predictably, without fighting your own body.
This material is for informational purposes and does not replace medical advice.
