Calorie deficit calculator

What is a calorie deficit?

A calorie deficit is the gap between the calories you burn and the calories you eat. Burn 2,200 and eat 1,700, and you're in a 500-calorie deficit. Your body covers the gap from its own stores, mostly body fat, and over time you lose weight.

The number you burn in a day is your maintenance calories, also called your TDEE. Eat that much and your weight holds. Eat less and you're in a deficit. Eat more and you're in a surplus.

How to calculate your calorie deficit

It takes three steps, and the calculator does all of them:

1. Estimate your resting calories (BMR). This calculator uses the Mifflin-St Jeor equation, which takes your sex, age, height and weight.
2. Multiply by your activity level to get your maintenance calories. The TDEE calculator covers this step in detail, including which activity level to pick.
3. Subtract your deficit: 500 calories a day for about 1 lb a week, or 1,000 for about 2 lb.

A worked example

A 35-year-old woman who is 5 ft 5 in, weighs 170 lb and is lightly active burns about 2,020 calories a day. To lose about 1 lb a week she'd eat 2,020 − 500 = 1,520 calories a day.

A 40-year-old man who is 5 ft 10 in, weighs 220 lb and is lightly active burns about 2,630 calories a day. His number is 2,130 calories to lose about 1 lb a week, or 1,630 to lose about 2 lb.

How many calories should I eat to lose weight?

It depends mostly on your size and how active you are, which is why one number doesn't fit everyone. These tables show daily calories at a few starting weights, for someone who is 35 and lightly active, calculated with the same function as the tool above. For your own number, use the calculator.

Women (5 ft 4 in, age 35, lightly active)

Men (5 ft 10 in, age 35, lightly active)

Calories a day, rounded to the nearest 10. * The daily minimum (1,200 for women, 1,500 for men): the pace is slower than 2 lb a week.

How big should your calorie deficit be: 1 or 2 pounds a week?

Most guidance lands on a deficit of 500 to 1,000 calories a day, which is about 1 to 2 lb a week. The math behind it is an old rule of thumb: a pound of body fat holds about 3,500 calories, so 500 a day adds up to a pound in seven days.

• A 500-calorie deficit (about 1 lb a week) is enough to lose weight and is the easier one to keep up. It's the default in the calculator.
• A 1,000-calorie deficit (about 2 lb a week) suits people with higher maintenance calories. If you burn 3,000 a day, it still leaves you 2,000 to eat. If you burn 1,900, it doesn't leave enough, and the calculator stops at the daily minimum instead.

The 3,500-calorie rule is a starting point, not a promise. It tends to overstate weight loss over months, because a lighter body burns fewer calories and the same meals become a smaller deficit.

How long will it take to reach your goal weight?

Add a goal weight and the calculator shows about how many weeks it takes and the month that lands in. It's mostly simple arithmetic: pounds to lose divided by your weekly pace. Losing 20 lb at 1 lb a week takes about 20 weeks.

Treat the date as an estimate. A few things move it:

• The first weeks often run fast. Some of the early drop is water, not fat.
• Loss slows as you get lighter. Your maintenance calories come down with your weight, so keeping the same pace means eating a little less over time. The timeline assumes you do, without ever going under the daily minimum.
• Weight doesn't fall in a straight line. It moves up and down by a pound or two from day to day. Watch the trend over two or three weeks.

Recalculate every 10 to 15 lb so your calories match your new weight.

Calorie deficit on a GLP-1: semaglutide and tirzepatide

Weight loss on a GLP-1 still comes from a calorie deficit. The medication doesn't replace it. It makes it easier to reach by lowering appetite, so you feel full on less food. That holds for semaglutide and tirzepatide alike, including the FDA-approved brands (Ozempic® and Wegovy® for semaglutide, Mounjaro® and Zepbound® for tirzepatide).

So the question changes. Without medication, most people use a calorie deficit calculator to find a ceiling. On a GLP-1, the number is more useful as a check that you're eating enough.

• How many calories should you eat on semaglutide or tirzepatide? There's no special number for the medication. Use the result above as a guide, and follow the plan you and your clinician agree on.
• Do you need to count calories? Not necessarily. Many people don't. Tracking for a week or two shows whether you're close to your number or well under it.
• Should you aim for the bigger deficit? A lower appetite can make 2 lb a week feel easy. A moderate deficit you can keep, with enough protein, is the safer default.

Medication is prescribed by a licensed clinician, who is the right person to ask how much you should be eating.

Eating too little: calorie minimums and protein

A bigger deficit isn't a better one. Eat too little and you can lose muscle along with fat, feel tired, and fall short on protein, vitamins and minerals.

A common rule is not to eat fewer than 1,200 calories a day for women or 1,500 for men unless a health professional is supervising. The calculator never suggests less. For a 35-year-old woman at 170 lb who is lightly active, a 2 lb a week pace would mean 1,020 calories, so the calculator shows 1,200 and a slower pace instead.

Protein matters more in a deficit, because it helps you keep muscle while you lose fat. Research on weight loss often points to about 0.5 to 0.7 grams of protein per pound of body weight a day, and the protein calculator turns that into grams for you. When your appetite is low, eat the protein on your plate first. Here's how much protein you need on a GLP-1.

Why am I not losing weight in a calorie deficit?

If the scale hasn't moved in two or three weeks, the deficit is usually smaller than it looks on paper. The common reasons:

• Untracked calories. Cooking oil, drinks, sauces, bites while cooking and weekends add up quickly.
• An activity level set too high. It's the easiest input to overestimate. Try one level lower.
• Water weight. Salt, hormones, a hard workout or constipation can hide fat loss for a week or two.
• An old number. After you lose 10 to 15 lb, your maintenance calories are lower. Recalculate.

On a GLP-1 and stalled? There's more in why you may not be losing weight on semaglutide. If your weight hasn't changed for a month, talk to your clinician.