What is a calorie deficit?

A calorie deficit means eating fewer calories than your body burns in a day. Your body makes up the difference by pulling energy from stored fat, and the scale goes down. That is the entire mechanism behind every successful fat-loss plan: keto, intermittent fasting, low-carb, high-protein, whatever the label. The food is just the wrapper. The deficit is the engine.

Two numbers matter: how many calories you burn (TDEE, total daily energy expenditure) and how many you eat. Subtract the second from the first and you get your deficit. A 500 kcal daily deficit for a week adds up to 3,500 kcal, which is roughly half a kilo of body fat. Keep it consistent and the pounds come off in the same predictable rhythm.

How many calories should you eat to lose weight?

It depends on your body, activity level, and how fast you want to lose. As a realistic starting point:

Most people do best with the moderate setting. A 500 to 600 kcal deficit is aggressive enough to show real change on the scale within 10 days, but gentle enough that energy, training, and mood stay intact. You rarely gain anything by going faster, and you frequently lose muscle, sleep quality, and adherence when you do.

How fast should you lose weight?

A practical ceiling is around 1 % of body weight per week. An 80 kg person can safely lose up to 0.8 kg per week for a few weeks at a time; a 100 kg person can push closer to 1 kg. Once you drop below that bodyweight, the same absolute rate becomes disproportionately aggressive and the muscle-preservation math gets worse.

Lean people (already under 15 % body fat for men, 22 % for women) should aim slower, around 0.5 % of bodyweight per week, because there is less fat to pull from and the risk of lean-tissue loss rises sharply as you get leaner.

Why your calorie deficit might not be working

If the scale is stuck in a deficit that should be working, the issue is almost always one of three things.

1. Tracking error

Packaged food labels are legally allowed to be ~20 % off. Restaurant meals are commonly 30 to 60 % higher than menu listings. Cooking oils, sauces, nut butters, and cheese are the biggest offenders because they are calorie-dense and easy to misjudge by eye. A cheap kitchen scale closes this gap fast.

2. Plateaus and water retention

Weight swings 0.5 to 1.5 kg day to day purely from water, sodium, glycogen, and gut contents. One high-sodium meal or a few extra carbs and the scale can jump by a kilo overnight even inside a deficit. The fix is a 7-day rolling average. If your 7-day average has not moved in 2 to 3 weeks, then you have a real plateau.

3. Metabolic adaptation

After a sustained deficit your body lowers its energy output by a few percent: BMR dips slightly, and more noticeably, non-exercise movement drops. You fidget less, stand less, take fewer steps. The effect is real and can erase 10 to 15 % of your deficit. Recalculate every 4 to 8 weeks during an active cut and adjust accordingly.

How to calculate your calorie needs more accurately

Every formula, including this one, is a population estimate with a ±10 % error bar for any individual. The only way to know your real numbers is to track. Log your intake for 14 to 28 days, weigh yourself daily, take a 7-day average, and back-calculate your real maintenance from the data. Our full TDEE calculator has an Adaptive Check mode that does this automatically.

Three habits that close the gap between estimate and reality:

• Weigh food when calories matter (oils, nuts, cheese, meat). Cups and spoons cannot see density.
• Weigh yourself daily at the same time, but only trust the 7-day average.
• Recalculate as you lose. A 90 kg body does not burn the same as an 80 kg body doing the same activity.

Is a bigger calorie deficit better?

No. Beyond a certain point, a bigger deficit costs you more than it gives. Deficits over ~1000 kcal per day for normal-weight people reliably lead to:

• Muscle loss, which lowers your TDEE further and makes the rest of the cut harder.
• Stronger hunger and cravings, which drive binges that wipe out a week of progress in a single sitting.
• Worse sleep and training performance, which compound over weeks.
• Sharper metabolic adaptation, so the deficit quietly shrinks and you stop losing while still eating too little.

The practical rule: keep the deficit at 0.5 to 1 % of bodyweight per week. If you want faster results than that, widen the deficit by burning more (walking, training, non-exercise activity), not by eating less.

FAQ

How accurate is this calculator?

This calculator gives you a practical starting point, not a guarantee. It uses equations validated across thousands of people (Mifflin-St Jeor and Katch-McArdle) and the 7700 kcal-per-kilo energy-balance model that underpins every credible fat-loss plan. For the average person it lands within roughly ±10 % of true maintenance.

Real results vary for three reasons we cannot model from a web form:

• Individual metabolic variation. Two people with identical age, weight, height, and activity can have resting rates that differ by 150 to 300 kcal per day.
• Non-exercise activity. Fidgeting, standing, and incidental walking can add or subtract 500+ kcal a day and are only partially conscious.
• Tracking accuracy on your end. Every calorie-dense food you eyeball becomes a source of hidden error that compounds over the week.

The best accuracy comes from using this number as a starting hypothesis, tracking your weight and intake for 2 to 4 weeks, and adjusting by about ±150 kcal based on the actual trend. The formulas give you the map. Your scale is the territory.

This tool is for educational and general-fitness use. It is not medical advice. If you have a history of disordered eating, a diagnosed metabolic condition, or are pregnant or breastfeeding, please work with a registered dietitian or physician rather than a calculator.