Calorie Deficit Calculator
This calorie deficit calculator estimates how many calories you burn in a day, subtracts the deficit you choose and shows the daily calorie target that's left. It also estimates how much weight you might lose per week and how many weeks it could take to reach your goal weight, with a table every four weeks. Treat it as a starting point: your body adapts, and real-world loss is usually slower.
Updated
Results
- TDEE (kcal per day)Mifflin-St Jeor × activity factor.
- Estimated loss per week
- Weight to lose
- Deficit applied (kcal per day)Smaller than entered if the floor applies.
- Calorie floor
- Deficit as % of TDEE
| Week | Estimated weight |
|---|
Results are estimates. See the methodology below.
How to use the calculator
- Keep US units (pounds, feet and inches) or switch to metric.
- Enter your sex, age (18 or older), current weight and height.
- Pick the activity level that matches a typical week, counting both your job and exercise. If you're unsure, choose the lower one.
- Enter a goal weight below your current weight.
- Set the daily deficit in calories, from 100 to 1,500. The default is 500.
The main results are your daily calorie target and the estimated number of weeks. Below them you'll see your TDEE, weekly loss, the deficit actually applied and the four-week table, in the unit you selected.
How it works
1. Total daily energy expenditure (TDEE)
Resting metabolic rate comes from the Mifflin-St Jeor equation (1990): 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 for men, or − 161 for women. Pounds and inches are converted first. That value is multiplied by an activity factor of 1.2, 1.375, 1.55, 1.725 or 1.9.
2. Calorie target and floor
Target = TDEE − deficit. If that falls below 1,200 calories for women or 1,500 for men, the calculator uses that floor instead and flags it. These floors are a common, conservative convention used by calculators, not a medical rule. When the floor applies, your real deficit is smaller and the timeline gets longer.
3. Weekly loss and timeline
The calculator uses the classic rule that 1 lb of body weight ≈ 3,500 calories (7,700 kcal per kg in metric): weekly loss = deficit × 7 ÷ 3,500. Weeks = pounds to lose ÷ weekly loss. The table steps that loss forward every four weeks until you reach the goal.
Examples
Woman, 35, 180 lb, 5 ft 5 in, lightly active, goal 160 lb
Estimated TDEE is 2,079 calories. With a 500-calorie deficit the target is 1,579 calories a day, 24.0% below TDEE. That's about 1.00 lb a week, so the 20 lb would take about 20 weeks on paper.
| Week | Estimated weight |
|---|---|
| 4 | 176.0 lb |
| 8 | 172.0 lb |
| 12 | 168.0 lb |
| 16 | 164.0 lb |
| 20 | 160.0 lb |
Man, 40, 220 lb, 5 ft 10 in, moderately active, goal 195 lb
TDEE of 2,967 calories. A 750-calorie deficit gives a target of 2,217 calories, about 1.50 lb a week and roughly 16.7 weeks for 25 lb.
When the floor kicks in
A 62-year-old woman who weighs 150 lb, is 5 ft 3 in and mostly sedentary burns about 1,451 calories. Subtracting 500 would go below 1,200, so the calculator shows 1,200 calories. The actual deficit is only 251 calories: about 0.50 lb a week and roughly 19.9 weeks to lose 10 lb.
Limits of the estimate
The 3,500-calorie rule is linear, and it overestimates long-term weight loss. Thomas and colleagues (2013) compared it with seven weight-loss experiments and concluded that it grossly overestimates actual loss; they recommend dynamic models instead. Hall and colleagues (2011) showed that body weight responds slowly to a change in intake, with a half time of about one year, and that people with more body fat take longer to reach a new stable weight. Your TDEE also drops as you lose weight, so rerun the numbers every few weeks.
Don't use this calculator if you're pregnant or breastfeeding, under 18, or have or have had an eating disorder. If you have a medical condition or take medication that affects your weight, talk to your doctor or a registered dietitian first.
Frequently asked questions
How big should my calorie deficit be?
There's no single right number. The calculator starts at 500 calories a day and accepts 100 to 1,500. Larger deficits are harder to sustain; a doctor or registered dietitian can tailor one to you.
How much weight will I lose with a 500-calorie deficit?
By the 3,500-calorie rule, about 1 lb a week. Over months, actual loss is usually less, because your energy needs fall as your weight does.
Why am I losing weight slower than the calculator says?
A lighter body burns fewer calories, and the linear rule doesn't capture that adaptation. Water and digestive contents also make the scale move from day to day.
What does the calorie floor message mean?
Your TDEE minus the deficit would land below 1,200 calories (women) or 1,500 (men). The calculator uses that floor and recalculates the timeline with the smaller deficit that remains.
How accurate is the Mifflin-St Jeor equation?
It's one of the most widely used equations for adults' resting metabolic rate, but it predicts an average. Your own number can differ, and the activity factor adds more uncertainty.
Is there a more accurate tool?
Dynamic models account for energy needs changing as weight changes. The NIH's National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) offers the Body Weight Planner, which lets you build a calorie and physical activity plan to reach a goal weight.
Sources
This is an estimate for healthy adults, not medical advice or a meal plan. Check with a healthcare professional before making major changes to your diet.