Convert between common food energy units.
A calorie is a unit of energy. In nutrition, when we talk about calories, we mean kilocalories (kcal) - the amount of energy required to raise the temperature of one kilogram of water by one degree Celsius. Every food and drink you consume contains a certain number of calories, which your body uses to fuel everything from breathing and circulation to exercise and digestion. When you consume more calories than your body needs, the excess is stored as fat. When you consume fewer, your body burns stored fat for energy - which is the fundamental principle behind weight loss.
Understanding how many calories your body needs each day is the foundation of any effective nutrition plan, whether your goal is to lose weight, gain muscle, or simply maintain your current weight.
Our free calorie calculator estimates your daily calorie needs based on your age, sex, height, weight, and activity level. It uses clinically validated formulas to calculate your Basal Metabolic Rate (BMR) - the number of calories your body burns at complete rest just to keep you alive - and then applies an activity multiplier to estimate your Total Daily Energy Expenditure (TDEE). Your TDEE is your maintenance calorie level: the number of calories you need to consume each day to stay at your current weight.
Once you know your TDEE, the calculator shows you adjusted calorie targets for weight loss, aggressive weight loss, weight gain, and mild weight gain, so you can choose the goal that fits your lifestyle.
There are several established formulas for estimating BMR. Our calorie calculator supports three of the most widely used:
Developed in 1990, the Mifflin-St Jeor equation is considered the most accurate BMR formula for most people. Research consistently shows it outperforms older formulas for the general population.
For example, a 35-year-old woman who weighs 70 kg and is 165 cm tall has a BMR of approximately 1,444 calories per day.
Originally published in 1919 and revised in 1984, the Harris-Benedict equation was the gold standard for decades. It tends to slightly overestimate calorie needs compared to Mifflin-St Jeor, but remains widely used.
Where W = weight in kg, H = height in cm, A = age in years.
The Katch-McArdle formula calculates BMR based on lean body mass rather than total body weight, making it potentially more accurate for athletes and muscular individuals who carry less body fat.
To use this formula, you need to know your body fat percentage. It is the most accurate option for lean, athletic individuals, but requires an additional measurement.
Your BMR is multiplied by an activity factor to estimate your TDEE. Choosing the right activity level is critical - most people tend to overestimate how active they are, which leads to overeating. The standard activity multipliers are:
When in doubt, choose the lower activity level. It is safer to underestimate and adjust upward based on real-world results than to overestimate and wonder why the scale isn't moving.
Calorie needs vary significantly based on individual factors including age, sex, body size, muscle mass, and activity level. According to the U.S. Department of Health and Human Services, general daily calorie guidelines for adults are:
These are broad ranges. A 5'4", 130-pound sedentary woman in her 50s may need only 1,600 calories to maintain weight, while a 6'2", 220-pound active man in his 20s may need 3,200 or more. This is why a personalized calorie calculator is far more useful than generic recommendations.
Harvard Health Publications recommends that women consume a minimum of 1,200 calories per day and men a minimum of 1,500 calories, unless under direct medical supervision. Going below these levels risks nutritional deficiencies, muscle loss, and metabolic slowdown.
The fundamental principle of weight loss is creating a calorie deficit - consuming fewer calories than your body burns. One pound of body fat contains approximately 3,500 calories. Therefore:
While this math provides a useful framework, actual weight loss is influenced by many other factors including water retention, hormonal fluctuations, sleep quality, stress levels, and the types of foods you eat. Do not expect perfectly linear results - weight can fluctuate by 2–4 pounds day-to-day based on hydration alone.
Gaining weight - particularly lean muscle mass - requires a calorie surplus. Consuming more calories than you burn gives your body the energy and building blocks needed to grow muscle tissue, especially when combined with resistance training. A modest surplus of 250–500 calories per day above your TDEE is generally recommended for lean muscle gain. Larger surpluses tend to result in more fat gain rather than additional muscle.
For those trying to gain weight due to illness, underweight status, or athletic goals, prioritizing calorie-dense, nutrient-rich foods is important. Focus on whole grains, lean proteins, healthy fats, dairy, and starchy vegetables rather than junk food, which adds calories but little nutritional value.
Calorie cycling - also called zigzag dieting - involves alternating between higher and lower calorie days throughout the week while keeping the weekly total at the same level. The idea is to prevent the body from adapting to a consistent deficit, which can slow metabolism over time.
For example, if your target is 14,000 calories per week (2,000/day average), you might eat 2,400 calories on three days and 1,775 calories on four days. This variation keeps the body from settling into a metabolic "set point" while still achieving the same average deficit. Some research suggests this approach can improve diet adherence by allowing higher-calorie days that feel more satisfying.
Not all calories are equal. While a calorie deficit drives weight loss regardless of food source, the types of food you eat have a profound impact on hunger, energy, body composition, and long-term health. Here's why food quality matters:
In practice, focusing on protein, vegetables, whole grains, and minimally processed foods makes it much easier to hit your calorie target while feeling satisfied - and ensures you're getting the nutrients your body needs.
Getting a feel for the calorie content of common foods helps you make informed choices throughout the day. Here are approximate values for frequently consumed foods:
These numbers can vary significantly based on preparation method, brand, and portion size. For accurate tracking, weigh your food with a kitchen scale and look up entries in a verified food database.
Exercise contributes to your total daily calorie burn, but typically less than most people assume. The calories burned during exercise depend on the type of activity, intensity, duration, and your body weight. Larger individuals burn more calories performing the same activity. Here are approximate hourly calorie burns for common activities:
A common mistake is to eat back all exercise calories logged in a fitness app, which often overestimates burn. If you selected an accurate activity level in our calorie calculator, your TDEE already accounts for your regular exercise. Additional eating on top of that can erase your deficit.
For most adults, 1,200 calories is the absolute minimum recommended for women, and 1,500 for men, according to Harvard Health. Eating below these levels risks nutritional deficiencies, significant muscle loss, and metabolic adaptation - where your body lowers its calorie burn in response to reduced intake. If your calculated deficit for losing 2 lbs/week falls below these minimums, choose a less aggressive goal instead.
Most people overestimate their activity level, which leads to overestimating calorie needs. A sedentary person who does occasional light walks is not "lightly active" - they are sedentary. Lightly active means deliberate exercise 1–3 days per week in addition to an otherwise low-activity lifestyle. When uncertain, choose the lower level and adjust based on your results after two to three weeks.
Several factors can cause slower-than-expected results: underreported food intake (the most common cause), overestimated activity level, water retention from hormonal changes or high-sodium meals, or metabolic adaptation over time. If you've been accurately tracking for 3–4 weeks without results, reduce your calorie target by 100–200 calories and reassess.
If you selected an activity level that accurately reflects your exercise habits, your TDEE already includes those calories burned. Eating them back would eliminate your deficit. The exception: if you chose "sedentary" as your base and then do additional exercise beyond your normal routine, a partial eat-back (50%–75% of estimated burn) may be appropriate.
The Mifflin-St Jeor equation is the most accurate BMR formula for the general population, with studies showing it is correct within approximately 10% for most people. However, individual metabolism varies based on genetics, muscle mass, gut microbiome, sleep, and other factors. Treat the result as a starting estimate and fine-tune it based on 2–4 weeks of real-world data.
Total calories determine whether you gain, lose, or maintain weight. But macronutrient composition - the ratio of protein, carbohydrates, and fat - significantly affects body composition (how much of the weight change is muscle vs. fat), hunger levels, energy, and long-term health. For most people aiming to lose fat while preserving muscle, a higher-protein diet (30%+ of calories) is well-supported by research.