Calorie Deficit Calculator for Weight Loss

Start with maintenance calories

Your maintenance calories, or total daily energy expenditure (TDEE), are what you burn in a normal day. The most widely validated estimate is the Mifflin-St Jeor equation for resting metabolic rate. Men: 10 × weight in kg + 6.25 × height in cm − 5 × age + 5. Women: the same, but − 161 instead of + 5. Multiply the result by an activity factor: 1.2 for sedentary, 1.375 for light exercise, 1.55 for moderate exercise three to five days a week, 1.725 for hard daily training.

Worked example: a 30-year-old man, 178 cm and 77 kg. 770 + 1,112.5 − 150 + 5 = 1,737.5 kcal resting. Moderately active: 1,737.5 × 1.55 = 2,693 kcal per day to maintain weight.

How big should the deficit be?

A deficit of 500 kcal a day is the classic starting point. The old rule says 3,500 kcal equals about one pound of fat, so 500 × 7 = 3,500 kcal, or roughly one pound per week. With a 2,400 kcal maintenance, that means eating about 1,900 kcal.

A useful ceiling is losing about 0.5 to 1 percent of body weight per week. For a 200-pound person, that is 1 to 2 pounds weekly. Faster than that and you lose more muscle, feel worse, and are more likely to rebound.

Common floors: most guidance suggests not going below about 1,200 kcal a day for women or 1,500 for men without medical supervision.

Why the 3,500 rule overestimates

The 3,500 kcal rule works for the first few weeks and then drifts. As you lose weight, you burn fewer calories: a smaller body costs less to run, and you tend to move less without noticing. Research models from the NIH suggest real-world loss over a year is often closer to half of what the simple rule predicts.

So a 500 kcal deficit that should produce 12 pounds in 12 weeks might produce 8 to 10. That is normal, not failure. Recalculate maintenance every 10 to 15 pounds lost.

Making a deficit sustainable

Protein: aim for about 0.7 to 1 gram per pound of goal body weight. It keeps you full and protects muscle. Strength training two to three times a week tells your body to keep the muscle it has. Fiber and volume, from vegetables, fruit, beans, and broth-based soups, make a smaller calorie budget feel larger.

Weigh daily if you like data, but judge progress by the weekly average. Day-to-day swings of 2 to 4 pounds from water and sodium are normal and meaningless.

Tracking calories accurately

Most people underestimate what they eat, often by 20 to 40 percent in studies. The usual culprits are cooking oil (about 120 kcal per tablespoon), sauces, drinks, and bites taken while cooking. A food scale for the first few weeks is the fastest way to calibrate your eye. After that, estimates get much better.

Exercise calories are overestimated too. Fitness trackers and gym machines can be off by 30 percent or more. If you eat back exercise calories, eat back about half. Better yet, set your activity level honestly in your maintenance estimate and do not add exercise on top.

Plateaus and diet breaks

If the weekly average has not moved for three to four weeks, first check tracking accuracy and water retention, which can mask fat loss, especially around a hard training block or a menstrual cycle. If it truly stalled, cut another 100 to 200 kcal or add daily steps. An extra 3,000 steps burns roughly 100 to 150 kcal for most adults.

Some people do well with a planned diet break: one to two weeks at maintenance after 8 to 12 weeks of dieting. It will not undo progress, and it often makes the next phase easier to stick with.

Using this calculator

Enter your maintenance estimate, your planned daily deficit, and the number of days in your plan. You get a daily calorie target, weekly and total deficits, and a 3,500-rule weight-loss estimate, plus a warning if the target drops below common safety floors. Expect the real result to be a bit slower than the estimate. This is an educational estimate, not medical advice; talk to a doctor or registered dietitian if you have a health condition, are pregnant, or have a history of disordered eating.