Calorie Deficit Calculator

How to use this calculator

Enter your current weight and goal weight, then pick a goal date. The start date defaults to today. Add your sex, age, height and activity level so the calculator can estimate how many calories you burn now. You’ll see:

• your daily calorie target and the daily deficit behind it
• your weekly loss rate, in pounds and as a percentage of your body weight
• your maintenance calories today and at your goal weight
• warnings if the pace or the calorie target looks too aggressive
• a projected weight chart and a week-by-week table you can download

Leave the goal date blank and the calculator plans for 16 weeks. If you don’t have a date in mind and just want a target for a steady pace, the calorie calculator shows every option from 0.5 to 2 lb a week.

The formula

First the calculator estimates your maintenance calories, or TDEE, from the Mifflin-St Jeor equation multiplied by an activity factor (the same method as our TDEE calculator). Then it spreads the energy needed to lose the weight evenly across the days until your goal date:

In metric units the same rule works out to about 7,716 calories per kilogram. The weekly loss rate is simply the total to lose divided by the number of weeks, and the safety check compares it with 1% of your current weight.

Worked example

A 35-year-old woman, 5 ft 5 in and 160 lb, lightly active, wants to reach 145 lb in 16 weeks (112 days).

1. Maintenance: her BMR is 1,422 calories, × 1.375 = 1,955 calories a day
2. Energy to lose: 15 lb × 3,500 = 52,500 calories
3. Daily deficit: 52,500 ÷ 112 = 469 calories
4. Target: 1,955 − 469 = 1,486 calories a day

That’s a loss of 0.94 lb a week, or 0.59% of her body weight, comfortably inside the usual range. Once she reaches 145 lb her maintenance drops to about 1,861 calories, which is roughly what she can eat to stay there.

Now suppose she wants the same 15 lb off in about six weeks, by December 20. That works out to 2.4 lb a week, 1.5% of her body weight, and a target of just 762 calories a day. The calculator flags both problems and suggests a date (January 11) that brings the pace down to 1% a week. Even then, her target would sit below the 1,200-calorie floor, so a later date still, or more daily activity, would be wiser.

Daily deficit by goal and timeline

This table shows the daily deficit needed for common goals. As a rough guide, anything above 1,000 calories a day, or faster than 2 lb a week, is too aggressive for most people.

The weekly pace follows the same pattern: 20 lb in 20 weeks is 1 lb a week, while 30 lb in 12 weeks is 2.5 lb a week. Whether a given pace is reasonable also depends on your size. One percent of body weight is 1.6 lb a week for a 160-lb person but 2.5 lb for someone who weighs 250 lb.

How fast is too fast?

The CDC recommends a gradual pace of about 1 to 2 pounds a week, noting that people who lose weight this way are more likely to keep it off. Researchers working with athletes suggest losing about 0.5% to 1% of body weight a week to hold on to muscle. This calculator warns you when your plan goes beyond 1% a week.

It also checks your calorie target against the commonly cited minimums of 1,200 calories a day for women and 1,500 for men (Harvard Health Publishing). Below those levels it’s hard to get enough protein and micronutrients, and hunger makes the plan harder to stick with.

Why the 3,500-calorie rule is only an approximation

The idea that a pound of fat holds about 3,500 calories is reasonable for a single pound. The trouble is applying it over months. As you lose weight you burn fewer calories at rest and during activity, so a fixed intake creates a smaller deficit each week. Researchers at the National Institutes of Health showed that the rule overestimates long-term weight loss and built the NIH Body Weight Planner to model the slowdown.

In practice that means:

• Expect the line to bend. Early weeks often drop faster (much of it water), and later weeks slower than the straight-line chart.
• Recalculate every few weeks with your new weight; your deficit target will rise slightly to stay on schedule.
• Protect muscle. A higher protein intake and strength training help. The macro calculator turns your calorie target into protein, carb and fat grams.

Assumptions and limitations

• Maintenance is estimated from the Mifflin-St Jeor equation and an activity multiplier, both of which can be off by 10% or more for an individual.
• The projection is a straight line; it doesn’t model metabolic adaptation, water weight or changes in activity.
• This calculator is for adults. It doesn’t apply during pregnancy or breastfeeding, or to anyone with a history of disordered eating.

Sources

• Centers for Disease Control and Prevention. Steps for Losing Weight.
• Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826–837.
• National Institute of Diabetes and Digestive and Kidney Diseases. Body Weight Planner.
• Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014;11:20.
• Harvard Health Publishing. Calorie counting made easy. Updated 2024.
• Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247.

These are general estimates for healthy adults, not medical advice. Talk to your doctor or a registered dietitian before starting a large or rapid weight-loss plan.

Updated November 2026. Results are estimates for educational purposes and depend on the inputs you provide.