Losing weight comes down to one simple idea with a few important details: you need to eat fewer calories than your body burns. The tricky part is knowing how many calories your body actually burns, and how big a gap is safe and sustainable. This guide walks you through the numbers, the science behind them, and how to set a target you can actually stick to.
How weight loss really works
Your body weight responds to energy balance: the difference between the calories you take in (food and drink) and the calories you burn (everyday living plus activity). This principle is recognized by health authorities including the National Institutes of Health (NIH).
- Eat more than you burn, and your body stores the surplus, mostly as fat.
- Eat less than you burn, and your body taps into stored energy to make up the difference.
- Eat roughly the same, and your weight stays stable.
To lose weight, you want to be in a calorie deficit: consistently eating a bit less than you burn. Everything else, from food choices to meal timing, mostly serves this one goal.
What is TDEE?
Your Total Daily Energy Expenditure (TDEE) is the total number of calories you burn in a day. It has a few parts:
- Basal metabolic rate (BMR): the energy your body uses at rest just to keep you alive, such as breathing, circulation, and cell repair. This is usually the largest piece.
- Physical activity: exercise plus general daily movement.
- The thermic effect of food: the calories burned digesting what you eat.
TDEE is the single most useful number for weight loss, because it tells you your maintenance level: the calories that keep your weight steady. Once you know it, you simply eat below it. You can estimate yours with our TDEE calculator.
How maintenance calories are estimated
Most reliable estimates start with the Mifflin-St Jeor equation, considered one of the most accurate formulas for predicting BMR in the general population. It works like this:
- For men: BMR equals 10 times weight in kg, plus 6.25 times height in cm, minus 5 times age in years, plus 5.
- For women: the same formula, but you subtract 161 instead of adding 5.
That gives your BMR. Multiply it by an activity factor (more for active people, less for sedentary) and you get your TDEE. You can run your resting number through our BMR calculator and let the tool handle the math.
Setting a safe calorie deficit
Once you know your maintenance calories, subtract a sensible amount. The widely recommended starting point is a deficit of about 300 to 500 calories per day.
A deficit in this range typically produces:
- Roughly 0.25 to 0.5 kg (about 0.5 to 1 lb) of weight loss per week.
- Steady, sustainable progress that is easier to maintain than aggressive cuts.
- Less muscle loss and fewer hunger spikes than crash dieting.
Larger deficits of 500 to 1,000 calories per day can produce faster loss (around 1 to 2 lb per week), but they are harder to sustain and carry more risk of muscle loss, fatigue, and nutrient gaps. Pick the gentlest deficit that still moves the scale. To dial in your exact target, try our calorie deficit calculator.
The 7700 kcal per kg rule (and its caveats)
A common rule of thumb says it takes about 7,700 calories to lose 1 kg of body fat (roughly 3,500 calories per pound). On paper, a 500-calorie daily deficit adds up to about 3,500 calories a week, or about half a kilogram.
This rule is a useful planning tool, but treat it as an approximation, not a guarantee. Real-world results differ because:
- Metabolism adapts. As you lose weight, your body becomes lighter and burns fewer calories, so the same diet creates a smaller deficit over time.
- Weight is not just fat. Early changes often include water and glycogen shifts, which can make the scale move faster or slower than the math predicts.
- Estimates are imperfect. Both calorie intake and calorie burn are hard to measure precisely.
Because of this, you should recalculate your targets every few weeks or after losing a noticeable amount of weight, and adjust based on what the scale actually does.
Minimum safe intake
Cutting calories too low backfires. As a general floor, most authorities, including guidance reflected by the Academy of Nutrition and Dietetics and the National Heart, Lung, and Blood Institute, advise not dropping below:
- About 1,200 calories per day for women.
- About 1,500 calories per day for men.
Below these levels it becomes very difficult to get enough protein, iron, calcium, folate, and vitamins C and D from food alone. Very low-calorie diets (under 800 calories per day) should only be followed under medical supervision.
Why crash diets backfire
Slashing calories far below your needs feels productive but usually undermines long-term results:
- You lose more muscle along with fat, which lowers your metabolism.
- Extreme hunger makes the plan nearly impossible to sustain.
- Rapid loss is often regained once normal eating resumes.
Slow and steady genuinely wins here. A modest deficit you can hold for months beats an aggressive one you abandon in two weeks.
Protein and keeping your muscle
When you eat in a deficit, you want the weight you lose to be fat, not muscle. Protein is your best protection.
- Adequate protein helps preserve lean muscle while you lose fat.
- It is also the most filling macronutrient, which helps control appetite.
- Combined with resistance training, protein helps maintain strength and metabolic rate.
A higher-protein intake is one of the most reliable levers for better body composition during weight loss. To set sensible protein, carb, and fat targets for your deficit, use our macro calculator.
Frequently asked questions
How many calories should I cut to lose weight?
Start by finding your maintenance calories (TDEE), then subtract about 300 to 500 per day. This usually yields around 0.25 to 0.5 kg (0.5 to 1 lb) of loss per week without leaving you exhausted or constantly hungry.
How fast can I safely lose weight?
For most people, about 0.5 to 1 lb (0.25 to 0.5 kg) per week is a safe, sustainable pace. Faster loss is possible with a larger deficit, but it raises the risk of muscle loss and is harder to maintain.
Is eating 1,200 calories a day enough?
For many women, around 1,200 calories is considered a sensible floor rather than a goal. Many people, especially men and active individuals, need more. Going lower than your recommended minimum without medical guidance risks nutrient deficiencies.
Why did my weight loss stall?
Plateaus are normal. As you get lighter, you burn fewer calories, so your old deficit shrinks. Recalculate your TDEE, double-check portion sizes, and consider adjusting your target or activity level.
This article is for general educational purposes only and is not a substitute for personalized advice from a qualified healthcare professional or registered dietitian.