Weight Loss Calculator

1. Pick US or metric units and your sex, then enter your age and height.
2. Enter your current weight, your goal weight and the number of weeks you want to take.
3. Choose your activity level now and the level you expect during the plan. The result updates as you type and flags any plan that is too fast or too low in calories.

A weight loss calculator is a planning tool that turns a goal weight and a timeline into an estimated daily calorie intake. It combines three numbers: the energy your body uses at rest, the extra energy your daily activity adds, and the calorie deficit needed to lose the weight in the time you chose.

It helps adults who want a realistic starting point before changing how they eat. It answers two questions at once: how much to eat, and whether the timeline is sensible. A 15 lb goal in 12 weeks is a 1.25 lb weekly pace, which sits inside the CDC range. The same goal in 4 weeks is 3.75 lb a week, which the tool flags as too fast.

A weight loss calculator is not a diet plan. It says nothing about food quality, protein, fibre or vitamins, and it cannot measure your metabolism. Use it with a BMI calculator to see where your current and goal weights fall, and talk to a clinician if you have a health condition.

The calculator estimates resting energy, scales it by an activity factor to get maintenance calories, and subtracts the daily deficit that your goal and timeline require.

1. Resting energy. Mifflin and colleagues built the equation in 1990 from 498 healthy adults aged 19 to 78, measured by indirect calorimetry. Their paper reported that the older Harris-Benedict equations overestimated measured resting energy by 5 percent.
2. Activity factor. The physical activity level (PAL) is total daily energy divided by resting energy. The National Academies 2023 energy report gives four PAL categories. The tool uses the typical value it lists for each: inactive 1.4, low active 1.6, active 1.75 and very active 2.05.
3. Deficit. The classic rule counts about 3,500 kcal per pound of body weight (about 7,700 kcal per kilogram). NHLBI guidance says a daily cut of 500 to 1,000 kcal gives about 1 to 2 lb a week.
4. Safety checks. A pace above 2 lb a week, or a target under 1,200 kcal a day, is shown as not recommended instead of as a target.

A 38-year-old woman is 65 in tall (165.1 cm) and weighs 180 lb (81.6 kg). She wants to reach 165 lb in 12 weeks. She is low active now and plans to add exercise, moving to the active level.

REE: 10 x 81.6 + 6.25 x 165.1 - 5 x 38 - 161 = 1,497 kcal/day. Maintenance now: 1,497 x 1.6 = 2,396 kcal. Maintenance during the plan: 1,497 x 1.75 = 2,620 kcal.

Deficit: 15 lb x 3,500 = 52,500 kcal over 84 days = 625 kcal/day. Target: 2,620 - 625 = 1,995 kcal/day. The pace is 1.25 lb (0.57 kg) a week, inside the CDC range, so the verdict is green.

At her goal weight, maintenance at the active level is about 2,501 kcal/day, roughly 119 kcal less than today. That gap is why the NIH says weight loss slows and why a lower weight needs a lasting change, not a short diet.

The equation gives an average for people like you, so real needs can sit well above or below the estimate.

Body Composition

Two people with the same height and weight can differ in muscle. The 1990 Mifflin study found fat-free mass was the best single predictor of resting energy, so a muscular person often needs more than the estimate.

Activity Level

The activity factor changes the result more than any other choice. Moving from inactive (1.4) to active (1.75) raises maintenance by 25 percent. The National Academies notes that its inactive group is not fully sedentary, so pick honestly.

Adaptation Over Time

As weight falls, resting energy falls too, and the body partly offsets the deficit. NIDDK explains that weight loss slows for this reason, which the simple 3,500 kcal rule does not capture.

Age and Sex

The equation drops 5 kcal a day for each year of age, and the female version is 166 kcal lower than the male version at the same size. For the resting number on its own, use the BMR calculator.

This page uses the 3,500 kcal rule because it is transparent and easy to check. The NIH Body Weight Planner uses a dynamic model instead. The table shows how they compare.

NIDDK says the 3,500 kcal rule has been used for decades, but the body responds to offset the deficit, so weight loss slows. Treat this calculator as a starting point and re-check it every few weeks.

Setting a Realistic Goal Date

Enter the goal and try different week counts until the verdict turns green. The row "Timeline at 1 to 2 lb a week" shows the range straight away.

Planning Added Exercise

Set the plan activity one step higher than today to see how much food the extra movement allows. To estimate a single workout, use the exercise calorie calculator.

Preparing for Maintenance

The maintenance-at-goal row shows the intake to hold the new weight. The CDC notes that even a 5 percent loss, such as 10 lb for a 200 lb person, can lower the risk of some chronic diseases.

1. Choosing a Timeline That Is Too Short

A short timeline pushes the deficit above 1,000 kcal a day. The tool flags it rather than printing an unsafe number.

2. Overstating Activity

Picking "very active" for a desk job with three workouts a week can add hundreds of calories to the target that you do not burn.

3. Expecting Straight-line Loss

The scale moves up and down from day to day, and NIDDK notes that loss slows over time. Judge progress over several weeks, not single weigh-ins.

4. Never Recalculating

Resting energy drops as weight drops. Re-enter your new weight every 4 to 6 weeks.

5. Mixing Units

Entering kilograms with the US setting gives a result that is badly wrong. Check the unit menu first.

The calculator is accurate to its equations, but the equations predict averages, so any single person can differ by hundreds of calories a day.

The CDC says people who lose about 1 to 2 pounds a week are more likely to keep the weight off than people who lose it faster. The calculator flags any plan above 2 lb a week.

About 500 kcal a day, using the 3,500 kcal per pound rule. NHLBI guidance links a 500 to 1,000 kcal daily cut to 1 to 2 lb a week.

Your body uses less energy as you get lighter and partly offsets the deficit. NIDDK researchers built the NIH Body Weight Planner to model this slowdown.

It will not show a target below 1,200 kcal a day. NHLBI says very low calorie diets under 800 kcal a day need monitoring by a doctor.

It is one of the better prediction equations for healthy adults, but it predicts an average. The 1990 study found Harris-Benedict overestimated measured resting energy by 5 percent.

Enter both. Maintenance now uses the current level, and the calorie target uses the level you expect to keep during the plan.

Yes, in this estimate, a higher activity level raises maintenance and the target. Workout calorie counts are estimates too, so do not eat back every calorie.

The CDC gives the example that a 5 percent loss, 10 lb for a 200 lb person, could lower the risk of heart disease, prediabetes and type 2 diabetes.

No. Pregnancy and breastfeeding change energy needs, and weight loss goals then need a clinician. The tool is also not for anyone under 18.

No. The calculation runs in your browser and nothing is sent to us. The Save button keeps a result only in this browser.

• Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals (1990) (American Journal of Clinical Nutrition, via PubMed, US National Library of Medicine).
• Dietary Reference Intakes for Energy: report highlights, PAL categories and Table 7-1 (National Academies of Sciences, Engineering, and Medicine, 2023).
• Steps for Losing Weight: 1 to 2 pounds a week (Centers for Disease Control and Prevention).
• NIH Body Weight Planner and the 3,500 calorie rule (National Institute of Diabetes and Digestive and Kidney Diseases, NIH).
• Aim for a Healthy Weight: calorie deficits and eating plan levels (National Heart, Lung, and Blood Institute, NIH).