How Many Calories Should I Eat to Lose Weight? A Simple Way to Find Your Number

How many calories should I eat to lose weight?

Most people can lose weight by eating about 20% below their maintenance calories. Maintenance is BMR from the Mifflin-St Jeor equation times an activity factor. For a lightly active 40-year-old woman who is 5 ft 5 in (165 cm) and weighs 170 lb (77 kg), that works out to about 1,590 calories a day.

You open a food app, it asks for a calorie goal, and you freeze. Is it 1,500? 1,800? 2,000? You don't need to guess. Your number comes from a short bit of math that takes about five minutes, or our calorie calculator can do the same steps for you.

Why is your calorie number personal?

Your calorie number depends on your size, age, sex, and how much you move. That is why a friend's number may not work for you.

Your body burns energy all day, even while you sleep. To lose weight, you eat a bit less than it burns. That gap is called a calorie deficit.

The trick is making the gap big enough to see progress. But it should be small enough that you can live with it.

How do you work out how many calories to eat to lose weight?

Use three steps: find your BMR, multiply it by your activity level, then take off about 20%. Here is each one.

1. Find your BMR (the calories you burn at rest).
2. Multiply by your activity level to get your maintenance calories.
3. Take off about 20% for weight loss.

Step 1: Find your BMR

BMR stands for basal metabolic rate. It is the energy your body uses just to keep you alive: breathing, pumping blood, keeping warm.

Most calculators, including ours, use the Mifflin-St Jeor equation. Researchers built it in 1990 from 498 healthy adults whose resting burn was measured in a lab.

A 2005 review for the American Dietetic Association looked at the common equations. It found Mifflin-St Jeor was the most likely to land within 10% of a person's measured resting burn.

Here is the formula. Use weight in kilograms, height in centimeters, and age in years.

• Women: (10 × weight) + (6.25 × height) - (5 × age) - 161
• Men: (10 × weight) + (6.25 × height) - (5 × age) + 5

To convert: 1 lb = 0.4536 kg, and 1 inch = 2.54 cm.

Step 2: Multiply by your activity level

Next, multiply your BMR by an activity factor. This gives your maintenance calories, also called TDEE (total daily energy expenditure). It is the amount that keeps your weight steady.

Be honest here. If you are stuck between two levels, pick the lower one. You can always adjust later. Our TDEE calculator shows your number at every level side by side.

Step 3: Take off about 20%

For weight loss, our calculators take 20% off your maintenance calories. So you multiply maintenance by 0.8. That's it. You have your starting number.

How many calories should a woman eat to lose weight?

A lightly active 40-year-old woman who is 5 ft 5 in and weighs 170 lb would start at about 1,590 calories a day. Here is the math for her, using 165.1 cm and 77.1 kg, the same formula our calculator uses:

• 10 × 77.1 = 771
• 6.25 × 165.1 = 1,031.9
• 5 × 40 = 200
• BMR = 771 + 1,031.9 - 200 - 161 = about 1,440 calories
• Maintenance = 1,441.9 × 1.375 = about 1,980 calories
• Weight-loss target = 1,982.6 × 0.8 = about 1,590 calories a day

That leaves plenty of room for real, filling meals.

How many calories should a man eat to lose weight?

A moderately active 45-year-old man who is 5 ft 10 in and weighs 200 lb would start at about 2,230 calories a day. He works out 3 to 5 days a week. In metric he is 177.8 cm and 90.7 kg:

• 10 × 90.7 = 907
• 6.25 × 177.8 = 1,111.3
• 5 × 45 = 225
• BMR = 907 + 1,111.3 - 225 + 5 = about 1,800 calories
• Maintenance = 1,798.3 × 1.55 = about 2,790 calories
• Weight-loss target = 2,787.4 × 0.8 = about 2,230 calories a day

Notice how much higher his number is. Cutting him to 1,500 would be a far bigger gap than the 20% plan calls for.

What if a 20% cut drops too low?

Our calculators never go below 1,200 calories a day for women or 1,500 for men. For smaller or older people, a 20% cut can drop under that line.

Take a 60-year-old woman who is 5 ft 0 in (152.4 cm), weighs 120 lb (54.4 kg), and is sedentary. Her BMR is about 1,040 calories. Her maintenance is about 1,240. A 20% cut would be about 990 calories.

In her case, the calculator shows 1,200 and flags that the floor was used. That floor is a safety line, not a target to aim for.

If your number lands near the floor, a slower pace or more daily movement may suit you better.

And talk to your doctor or a registered dietitian before cutting calories if you:

• are pregnant
• have diabetes or kidney disease
• take medicines that affect appetite or blood sugar
• have a history of an eating disorder

How fast will you lose weight?

Slower than the old math says. The CDC says people who lose about 1 to 2 pounds (0.5 to 0.9 kg) a week are more likely to keep it off.

Here's the thing. The old rule says 3,500 calories equals 1 pound (0.45 kg) of fat. It is easy math, but it is not the full story.

A 2011 study in The Lancet by Kevin Hall and colleagues at the National Institutes of Health looked at this. It showed that body weight responds slowly to a change in eating. Their model found half times of about 1 year.

In plain words, as you lose weight, you burn a little less. So weight loss slows over time. The simple 3,500 rule tends to overestimate how much you will lose in the long run.

For a more realistic forecast, the NIH Body Weight Planner is built on Hall's model.

The CDC also gives a helpful example. For a person who weighs 200 lb (91 kg), a 5% loss is 10 lb (4.5 kg). That change could lower the risk for some chronic diseases such as heart disease, prediabetes, and type 2 diabetes.

That is a win to feel good about, even if the scale never hits some "perfect" number.

How much protein should you eat while cutting calories?

The International Society of Sports Nutrition says 1.4 to 2.0 g of protein per kg of body weight a day is enough for most people who exercise. Protein helps you keep muscle while you eat less.

For a 170 lb (77 kg) person, that is about 108 to 154 g a day. That sounds like a lot. But a few smart swaps make it easy. Our protein calculator gives you a daily target for weight loss.

Eating out on a calorie target

You don't have to cook every meal. A few chain orders fit a calorie target well:

See more in our list of top protein picks at fast food chains.

What if your calorie target isn't working?

Treat your number like a first draft and adjust it after 2 to 3 weeks. The formula is a starting point, not a final answer.

The Frankenfield review found Mifflin-St Jeor was the most reliable common equation. But the authors also warned it can be off for some people. Older adults and some ethnic groups were underrepresented in the research.

So here is the plan:

1. Eat at your target for 2 to 3 weeks.
2. Weigh yourself a few mornings a week and look at the weekly average, not single days.
3. If your average hasn't moved, lower your target by about 100 to 200 calories (never below the floor), or add more walking.
4. If you are losing faster than 2 lb (0.9 kg) a week and feel worn out, eat a bit more.

Once you do this once, it becomes second nature. Want to understand the gap itself in more depth? Read our guide on how to calculate a calorie deficit.

My take

I like the 20% approach because it scales with you. A tall, active man and a petite, sedentary woman get very different numbers. That is exactly how it should be. A fixed "eat 1,200 calories" rule ignores all of that.

The part people skip is step 4, the adjusting. In my view, that is where real progress happens.

The bottom line

Find your BMR, multiply by your activity level, and take off about 20%. Your friend's number doesn't matter. Your own number is the one that counts.

Plug your details into our calorie calculator, give it a few weeks, and adjust. You've got this.