Calorie Calculator

The Mifflin-St Jeor formula, published in 1990, is widely considered the most accurate BMR equation for most people. For men it is: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age (years) + 5. For women it is: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age (years) - 161. It uses weight, height, age, and sex as inputs and has been validated against indirect calorimetry in multiple studies. This calculator uses the Mifflin-St Jeor equation exactly as published.

After calculating your BMR, the calculator multiplies it by an activity factor to estimate TDEE. The factors are: Sedentary (1.2) for desk jobs with little exercise; Lightly active (1.375) for light exercise one to three days per week; Moderately active (1.55) for moderate exercise three to five days per week; Very active (1.725) for hard training six to seven days per week; Extra active (1.9) for very intense training or a physically demanding job. Most people should start with Moderately active and adjust based on their real-world results over two to three weeks.

A deficit of 500 calories per day below your TDEE typically produces roughly 0.45 kg (1 lb) of fat loss per week, because one pound of fat contains approximately 3,500 calories. A milder deficit of 250 calories per day results in about half a pound per week. Larger deficits can accelerate losses in the short term but risk muscle loss, nutrient deficiencies, and metabolic adaptation. Most dietitians recommend a deficit of 300 to 500 calories per day as the sustainable sweet spot.

The 3,500-calorie rule is a long-standing rule of thumb stating that a deficit or surplus of 3,500 calories equals roughly one pound of fat gained or lost. It originates from research in the 1950s estimating the energy density of adipose tissue. While useful as a starting point, the rule is a simplification. In practice, weight change is not perfectly linear because the body adapts its metabolism, hormones, and muscle retention over time. The rule is most reliable over short periods for people who are not severely obese.

Macronutrients are the three classes of calorie-providing nutrients: protein (4 kcal per gram), carbohydrate (4 kcal per gram), and fat (9 kcal per gram). Total calories determine whether you gain, maintain, or lose weight. The split between macros affects body composition, satiety, muscle retention, and hormonal balance. The 30/40/30 split used in this calculator (protein/carbohydrate/fat) is a balanced general-purpose starting point. Athletes, diabetics, and people with specific health goals often use different ratios under professional guidance.

Several factors cause real-world results to differ from calculated estimates. The Mifflin-St Jeor formula was derived from population averages, so individuals with unusual muscle-to-fat ratios, thyroid conditions, or other metabolic factors may deviate significantly. Activity multipliers are also averages and do not capture the actual variation in how people move through the day. Additionally, food labels and restaurant portions carry their own measurement errors. Treat the calculator output as a starting estimate, then track your weight for two to three weeks and adjust your intake up or down accordingly.

To preserve muscle during a fat-loss phase, keep your protein intake high (at least 1.6 to 2.2 g per kg of body weight per day), use a moderate rather than aggressive calorie deficit (250 to 500 kcal below TDEE), and include resistance training in your routine. This calculator's macro table shows grams of protein at the 30 percent share, which is a reasonable minimum. Increasing protein to 35 or 40 percent at the expense of carbohydrates is a common adjustment for people prioritising lean body composition.

Yes. BMR declines gradually with age, primarily because people tend to lose muscle mass as they get older, and muscle tissue is metabolically more active than fat tissue. The Mifflin-St Jeor formula directly incorporates age as an input, so the calculator accounts for this. Beyond the formula, older adults often have lower activity levels and different hormonal profiles. Resistance training and adequate protein intake are the two most effective strategies for slowing the age-related decline in resting metabolic rate.

Eating below your BMR is generally not recommended for extended periods. BMR represents the minimum energy your body needs to keep vital organs functioning. Chronic intake below BMR can lead to muscle loss, nutrient deficiencies, fatigue, hormonal disruption, and metabolic slowdown. Very low-calorie diets (below 800 kcal per day) should only be undertaken under direct medical supervision. For sustainable fat loss, aim to eat between your BMR and TDEE, creating a deficit from your maintenance level rather than cutting below resting needs.

Yes, this calculator is completely free to use. There is no account to create, nothing to install, and no payment required. All calculations run instantly in your browser using the Mifflin-St Jeor formula. Your personal data, including your age, weight, and height, is never sent to a server or stored anywhere. You can adjust any input and see updated results in real time.

Recalculate your TDEE whenever your weight changes by more than 2 to 3 kg (4 to 7 lb), when your activity level changes significantly, or when you notice your weight has plateaued despite following your calorie target. As you lose weight, your BMR decreases because you are carrying less body mass, so the calorie target that produced a deficit initially will produce a smaller deficit or none at all over time. Recalculating every four to six weeks during an active diet phase keeps your targets accurate.