Introduction
Losing weight comes down to one simple idea: you need to burn more calories than you eat. But figuring out exactly how many calories to eat each day can be tricky. That's where our Weight Loss Calculator helps. It takes your age, height, weight, gender, and activity level, then uses proven formulas to estimate how many calories your body burns each day. From there, it builds a personalized plan that shows you the daily calorie target you need to reach your goal weight in your chosen time frame.
This calculator does more than just give you a single number. It estimates your Basal Metabolic Rate (BMR), which is the energy your body uses at rest, and your Total Daily Energy Expenditure (TDEE), which includes calories burned through daily activity and exercise. It then calculates the calorie deficit or surplus you need, breaks down suggested protein, carb, and fat ranges, and projects your weight change week by week. You can also turn on features like metabolic adaptation, which accounts for how your metabolism slows as you lose weight, and zigzag calorie cycling, which varies your daily intake to help you stay on track.
Whether you want to lose weight, gain weight, or maintain your current weight, this tool gives you a clear, data-driven starting point. Just enter your details, choose your goal, and hit calculate to get your full personalized plan with charts and weekly breakdowns.
How to Use Our Weight Loss Calculator
Enter your personal details, weight loss goal, and activity level below. The calculator will show you how many calories to eat each day, your BMR, TDEE, macronutrient ranges, and a week-by-week projection of your weight change.
Gender: Select whether you are male or female. This matters because men and women burn calories at different rates.
Age: Enter your current age in years, between 15 and 100. Your metabolism slows down as you get older, so age plays a big role in how many calories you burn. The Mifflin-St Jeor equation was derived on adults aged 19 to 78, so ages outside that range extrapolate.2
Height: Choose your preferred unit (feet and inches, centimeters, or meters), then enter your height. The calculator uses your height to figure out your base calorie burn.
Current Weight: Enter how much you weigh right now in either pounds or kilograms. This is the starting point for all calculations.
Body Fat % (Optional): If you know your body fat percentage, enter it here. This unlocks the Katch-McArdle formula, which uses your lean body mass to give a more accurate calorie estimate. If you don't know your body fat percentage, you can use our Body Fat Calculator to get an estimate.
Goal Direction: Pick whether you want to lose weight, gain weight, or maintain your current weight. This tells the calculator which direction to adjust your calories.
Target Weight: Enter the weight you want to reach in pounds or kilograms. This field only appears if you chose to lose or gain weight.
Time to Achieve Goal: Enter how long you want to take to reach your target weight. You can set this in days, weeks, or months. If the rate comes out faster than 2 pounds per week, a warning will appear because very fast weight change can be unhealthy.
Daily Activity Level: Choose the option that best matches how active you are each day. Options range from no activity at all up to very intense daily exercise or a physical job. This multiplier is applied to your BMR to calculate your total daily energy expenditure.
BMR Formula: Pick the formula used to estimate your basal metabolic rate. Mifflin-St Jeor is the recommended default for most people. Revised Harris-Benedict is an older alternative. Katch-McArdle requires a body fat percentage to work.
Metabolic Adaptation: Toggle this on to account for how your metabolism slows down as you lose weight. This gives you a more realistic projection over time.
Zigzag Calorie Cycling: Toggle this on to see a plan that varies your daily calories throughout the week while keeping the same weekly total. Some people find it easier to stick with higher-calorie days mixed in with lower-calorie days.
Weight Loss Calculator – How It Works
Weight loss happens when you burn more calories than you eat. This is called a calorie deficit. Our weight loss calculator figures out exactly how many calories you need each day to reach your goal weight in the time frame you choose. It uses your age, gender, height, weight, and activity level to give you a personalized plan.
Understanding the Key Numbers
The calculator starts by finding your Basal Metabolic Rate (BMR). Your BMR is the number of calories your body burns just to stay alive: breathing, pumping blood, and keeping your organs working. Even if you stayed in bed all day, your body would still burn this many calories.
Next, it calculates your Total Daily Energy Expenditure (TDEE). This takes your BMR and multiplies it by an activity factor based on how much you move each day. Your TDEE is the total number of calories you burn in a full day, including exercise and daily activities. To lose weight, you need to eat fewer calories than your TDEE. To gain weight, you need to eat more.
BMR Formulas Explained
The calculator offers three proven formulas for estimating BMR:
- Mifflin-St Jeor: This is the most widely recommended formula for most adults. It uses your weight, height, age, and gender, and was derived in 1990 from 498 healthy adults aged 19 to 78.2 A systematic review found it the most reliable of the common equations.7
- Revised Harris-Benedict: This is an updated version of one of the oldest BMR equations, first published in 1918.3 Roza and Shizgal re-fitted it in 1984.4 The coefficients here are those 1984 values as printed in a 2021 systematic review of prediction equations.5 In the Mifflin-St Jeor study the original equations overestimated measured resting energy expenditure by 5%.2
- Katch-McArdle: This formula uses your lean body mass instead of total body weight, which means you need to know your body fat percentage. Its published form is Cunningham's 1991 equation, 370 + 21.6 × lean body mass in kilograms.6 It can be more accurate for people who are very muscular or who know their body composition.
The 3,500-Calorie Rule
A widely used guideline in weight management is that one pound of body fat contains roughly 3,500 calories; Kevin Hall's analysis of the rule found it roughly right for people with a large initial fat mass and an overestimate for leaner people.8 So to lose one pound per week, you would need a daily deficit of about 500 calories (500 × 7 = 3,500). The calculator uses this rule to determine your daily calorie target based on how much weight you want to lose and how quickly you want to lose it.
Metabolic Adaptation
As you lose weight, your body gets smaller and needs fewer calories. This is called metabolic adaptation. When you enable this option, the calculator recalculates your BMR and TDEE each week based on your projected weight. This gives you a more realistic picture of your progress, since your calorie needs will naturally decrease over time.
Zigzag Calorie Cycling
Zigzag calorie cycling means eating more calories on some days and fewer on others, while keeping your weekly total the same. For example, you might eat more on workout days and less on rest days. Some people find this approach easier to stick with because they don't feel restricted every single day. The weekly average stays on track with your weight loss goal.
Safe Rates of Weight Loss
Guidance from the U.S. National Library of Medicine is that losing more than 1 to 2 pounds per week is not safe for most people, which makes that range the sensible ceiling.1 Losing weight faster than this can lead to muscle loss, nutritional deficiencies, and a slower metabolism. The calculator will warn you if your plan exceeds 2 pounds per week. It also sets a calorie floor of 1,500 calories for men and 1,200 calories for women. The National Heart, Lung, and Blood Institute's guide describes supervised low-calorie diets of 1,000 to 1,200 calories per day for most women and 1,200 to 1,600 for men; the calculator's floors sit at the bottom of those ranges.9
Macronutrients: Protein, Carbs, and Fat
The calculator also provides suggested ranges for your three main macronutrients. Protein (25–35% of calories) helps preserve muscle during weight loss and keeps you feeling full. Carbohydrates (40–55% of calories) give your body and brain energy. Fat (20–35% of calories) supports hormone production and helps your body absorb vitamins. These ranges can be adjusted based on personal preference or a dietitian's advice.
Important Things to Keep in Mind
This calculator provides estimates, not exact numbers. Every person's body is different, and factors like genetics, sleep, stress, medications, and hormonal changes can all affect weight loss. The numbers are a helpful starting point, but real-world results may vary. Staying well hydrated is also important during any weight loss plan. Our Water Intake Calculator can help you figure out how much water you should be drinking daily. If you have a medical condition or need to lose a significant amount of weight, talk to a doctor or registered dietitian before starting any plan.