How Many Calories Should I Eat to Lose Weight? The Deficit Math

If you are trying to lose weight, the question “how many calories should I eat?” has a concrete answer: the number is below your maintenance calories, but not below your body’s safety floor. This guide walks through the deficit math step by step. It is educational information, not medical advice.

The calorie chain: BMR × activity multiplier = TDEE

Your calorie needs start with your BMR, or basal metabolic rate: what you burn at rest just keeping your organs, muscles, and body temperature running. That number does not include walking, work, exercise, or even digesting food. It is your baseline.

Then you multiply BMR by an activity multiplier to get your TDEE, or total daily energy expenditure. TDEE is what you burn living your actual life: commuting, standing, working, working out, and recovering.

Think of it as a chain:

• BMR — what you burn at rest
• × activity multiplier — how much your daily movement adds
• = TDEE — what you burn living your life

TDEE is your maintenance number. Eat around it, and your weight should stay fairly stable. Eat below it, and weight trends down over time. Eat above it, and weight trends up. The math is a compass, not a contract.

The deficit steps: 250 and 500 kcal a day

The standard deficit steps are 250 kcal per day and 500 kcal per day. The 500-kcal step gets the most attention because of a common rule of thumb: a pound of body fat stores roughly 3,500 kcal. Spread that over seven days, and a 500-kcal daily deficit works out to roughly a pound a week.

That is theory. Real bodies are noisier than the math. Water shifts, hormonal changes, metabolic adaptation, and imperfect tracking all affect what the scale shows. Treat the rate as an estimate to check against the scale over weeks, not a promise per week.

Worked example: 35 years old, 70 kg, 165 cm

Let’s run the numbers for a 35-year-old woman who is 70 kg and 165 cm. Her Mifflin-St Jeor BMR calculation is:

10 × 70 + 6.25 × 165 − 5 × 35 − 161 = 1,395.25

That is about 1,395 kcal/day at rest.

Her TDEE changes with her activity level:

At moderate activity, her maintenance number is 2,163 kcal/day. If she subtracts 500 kcal, her target is about 1,663 kcal/day — roughly a pound a week in theory. If she subtracts 250 kcal, her target is about 1,913 kcal/day — roughly half a pound a week.

Now look at the sedentary case. If she has a desk job and is mostly inactive, her maintenance TDEE is 1,674 kcal/day. A 500-kcal deficit would put her at 1,174 kcal/day. That is below the safety floor for women, so the target becomes 1,200 kcal/day. The real deficit is about 474 kcal/day. The floor is doing its job.

The safety floors

Our Calorie Calculator never targets below 1,200 kcal/day for women or 1,500 kcal/day for men. If the arithmetic lands under a floor, the floor wins and the deficit shrinks.

That is not an arbitrary punishment. Below those levels, it becomes genuinely hard to get enough protein, vitamins, minerals, and total nutrition from ordinary food. The floor protects the deficit from turning into a crash.

Why the sedentary line traps people

The sedentary multiplier makes TDEE low. A desk job, long commute, and little structured movement can leave very little room between maintenance and the safety floor. That means an aggressive 500-kcal deficit collides with the floor quickly.

The fix is not eating below the floor. The fix is one of two things:

• A smaller deficit and more patience. On a sedentary TDEE, a 250-kcal deficit may be much more realistic.
• More movement. Walking, standing breaks, or structured exercise can raise the activity multiplier and give the deficit more room.

If you are sedentary and the math will not support a 500-kcal deficit above the floor, choose a smaller target or add activity. Do not treat the floor as a suggestion.

After the target: protect muscle with protein

Once you have a calorie target, the next question is how to split those calories. In a deficit, protein is the macro that protects muscle. You want enough protein to support lean tissue while you lose weight.

Our balanced split is 30% protein / 40% carbs / 30% fat. On the moderate-activity example above, maintenance is 2,163 kcal/day. That split gives about:

• 162 g protein
• 216 g carbs
• 72 g fat

That is the maintenance macro layout. For a deficit target, the same 30/40/30 percentages apply, but the grams come down with the calorie total. The Macro Calculator turns any calorie target into grams on the split you pick, including keto.

The calculators that run this chain

You do not need to do the arithmetic by hand every time. The Calorie Calculator runs the whole chain: maintenance, goal targets at the standard 250 and 500 kcal steps, the safety floors, and the macro split. If you want to see the range across BMR formulas, the BMR Calculator shows all three BMR formulas side by side.

When to stop and get a professional

This page is educational information, not medical advice. Stop and talk with a clinician or registered dietitian — not a web page — if any of these apply:

• Pregnancy
• A history of eating disorders
• Diabetes or other medical conditions
• Medication that affects weight
• Any plan to eat below the 1,200 or 1,500 kcal floors

A professional can help you set a safe target, account for your medical history, and adjust as your body responds.