How to calculate a calorie deficit to lose weight safely

To calculate a calorie deficit, estimate your maintenance calories, then eat less than that. Maintenance calories (your TDEE) are your resting burn from the Mifflin-St Jeor equation multiplied by an activity factor. Eating about 500 calories a day below that number is the usual starting point. It works out to roughly a pound a week at first, within the 1–2 pounds a week that the CDC calls gradual and steady.

That's the short version. The rest of this guide covers the working. It shows how to run the formula in pounds and inches, how big a deficit is sensible, three worked examples, and why the scale slows down even when you do everything right.

Step 1: Estimate your resting calories (BMR)

Your basal or resting metabolic rate (BMR) is roughly what your body burns at rest. The Mifflin-St Jeor equation, published in 1990, is a widely used way to estimate it. The authors measured resting energy expenditure in 498 healthy adults aged 19 to 78 and fitted this formula to the results:

Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161

The equation uses metric units, so convert first. Kilograms = pounds × 0.45359237 and centimeters = inches × 2.54. For example, 5 ft 5 in is 65 inches, or 165.1 cm. The pounds to kilograms converter and feet to centimeters converter show those steps.

In the original study the equation explained about 71% of the differences in measured resting burn between people. So your true number can sit above or below the estimate. Use it as a starting point and let your own results correct it.

Step 2: Multiply by an activity factor (TDEE)

Total daily energy expenditure (TDEE) adds everything you burn by moving. Most calculators, including ours, multiply BMR by one of the conventional activity factors below. They are rules of thumb rather than measured values. If you're between two levels, pick the lower one.

Compare your result with a national benchmark. The Dietary Guidelines for Americans, 2020–2025 estimated that adult women need roughly 1,600–2,400 calories a day and adult men roughly 2,000–3,000. Needs are lower for older, smaller and less active people and higher for younger, larger and more active people. If your result is far outside those ranges, double-check your inputs and activity level.

Step 3: Choose a deficit

The 2013 obesity guideline from the American Heart Association, American College of Cardiology and The Obesity Society offers two ways to set a weight-loss intake. You can cut 500 or 750 calories a day from your needs. Or you can eat about 1,200–1,500 calories a day for women or 1,500–1,800 for men, adjusted for body weight. The table shows what the old “3,500 calories per pound” rule predicts for the first weeks.

Bigger isn't automatically better. The CDC notes that people who lose weight at about 1–2 pounds a week are more likely to keep it off than people who lose it faster. Very-low-calorie diets (about 800 calories a day or less) are a medical treatment, meant to be used only under a doctor's supervision.

Worked examples

These use the same formula and activity factors as our calculator, rounded at the end.

Example 1: 35-year-old woman, 5 ft 5 in, 170 lb, lightly active

Weight: 170 × 0.45359237 = 77.11 kg Height: 65 × 2.54 = 165.1 cm BMR = 10 × 77.11 + 6.25 × 165.1 − 5 × 35 − 161 = 771.11 + 1,031.88 − 175 − 161 ≈ 1,467.0 kcal TDEE = 1,467.0 × 1.375 ≈ 2,017 kcal Target with a 500-kcal deficit = 2,017 − 500 = 1,517 kcal/day

That's roughly a pound a week to begin with. The CDC points out that losing even 5–10% of your body weight can bring health benefits. For her, that means a first goal of 8.5–17 pounds.

Example 2: 45-year-old man, 5 ft 10 in, 220 lb, desk job

Weight: 220 × 0.45359237 = 99.79 kg Height: 70 × 2.54 = 177.8 cm BMR = 10 × 99.79 + 6.25 × 177.8 − 5 × 45 + 5 = 997.9 + 1,111.25 − 225 + 5 ≈ 1,889.2 kcal TDEE = 1,889.2 × 1.2 ≈ 2,267 kcal 500-kcal deficit → 1,767 kcal/day 750-kcal deficit → 1,517 kcal/day

Both targets sit inside the guideline's 1,500–1,800 range for men. Adding a daily walk and switching to the “lightly active” factor would raise his TDEE to about 2,598. He could then reach the same deficit while eating more.

Example 3: 62-year-old woman, 5 ft 2 in, 150 lb, sedentary

Weight: 150 × 0.45359237 = 68.04 kg Height: 62 × 2.54 = 157.48 cm BMR = 10 × 68.04 + 6.25 × 157.48 − 5 × 62 − 161 = 680.39 + 984.25 − 310 − 161 ≈ 1,193.6 kcal TDEE = 1,193.6 × 1.2 ≈ 1,432 kcal 500-kcal deficit → 932 kcal/day (below the 1,200 guideline floor)

This is where a fixed 500-calorie cut breaks down. Smaller, older and less active people have lower maintenance needs, so the usual deficit pushes intake too low. A better plan is to eat around 1,200 calories and move more. At the “lightly active” factor her TDEE becomes 1,193.6 × 1.375 ≈ 1,641, which is a deficit of about 441 calories. That's slower than a pound a week, and that's fine.

Why the scale doesn't drop in a straight line

The 3,500-calorie rule assumes your calorie needs stay fixed. They don't. A smaller body burns less, so a fixed intake gives you a shrinking deficit.

• Your maintenance number falls as you lose. In Example 1, after losing 20 pounds (now 150 lb) her BMR drops to about 1,376 and her TDEE to about 1,892. Eating 1,517 calories now creates a deficit of about 375, not 500. Recalculate after every 10–15 pounds.
• Real curves bend. A 2011 analysis in The Lancet by NIH researcher Kevin Hall and colleagues gives a rule of thumb for adults with overweight. Every 10 calories a day of lasting change eventually moves body weight by about 1 pound, with half of the change after about a year and 95% after about three years. By that estimate, a lasting 500-calorie cut leads to about 50 pounds in total, roughly half of it in the first year. The 3,500 rule predicts 52 pounds in the first year alone (500 × 365 ÷ 3,500), and more after that.
• Daily weigh-ins are noisy. Water and the food you're carrying move the scale from day to day. Compare weekly averages, and give any change three to four weeks before you judge it.

If you want a forecast that includes this slowdown, the NIH's Body Weight Planner is built on the Hall model. It's designed for adults, not for pregnant or breastfeeding women.

Making the deficit easier to keep

• Move more, not just eat less. The Physical Activity Guidelines for Americans recommend 150–300 minutes a week of moderate aerobic activity, plus muscle-strengthening activity on 2 or more days. Activity also raises the TDEE your deficit is based on.
• Plan your protein. The Dietary Guidelines for Americans, 2025–2030 set a protein goal of 1.2–1.6 g per kilogram of body weight a day. For the 170-lb woman in Example 1, that's about 93–123 g.
• Track trends, not single days. Weigh yourself at the same time of day. When the weekly average stalls for a month, recalculate before cutting further.
• Look beyond the scale. Body composition changes too. Our guide to healthy body fat percentages explains how to track fat rather than just weight. You can check your starting point with the BMI calculator and ideal weight calculator.

Limits of this method

Everything here estimates averages for healthy adults. It doesn't apply to children and teens or during pregnancy or breastfeeding. It may not fit people with medical conditions or on medicines that affect weight. The CDC notes that medicines, medical conditions, stress, genes, hormones and age all influence weight. If any of these apply to you, or if you have a history of disordered eating, work out a plan with your doctor or a registered dietitian rather than a formula.