One input, BMI · BMR · TDEE all at once.

What the three numbers do—and do not—tell you

BMI, BMR, and TDEE answer different questions. BMI compares weight with height; it is a screening measure, not a diagnosis of body fat or health. The number labeled BMR here is an equation-based estimate of energy use at rest, not a direct metabolic measurement. TDEE multiplies that estimate by the activity factor you select. It approximates daily energy expenditure; it is not a recommended calorie intake.

Which BMI bands does this page use?

BMI equals weight in kilograms divided by height in meters squared. The English tool uses CDC adult categories:

• Underweight: below 18.5
• Healthy weight: 18.5 to less than 25
• Overweight: 25 to less than 30
• Obesity class 1: 30 to less than 35
• Obesity class 2: 35 to less than 40
• Obesity class 3: 40 or above

CDC describes these as adult categories for ages 20 and older. Children and teens through age 19 require age- and sex-specific BMI percentiles instead; do not interpret this page's adult category for someone aged 18 or 19. The numeric BMI itself does not separate muscle from fat or show where fat is stored. Medical history, examination, and other findings matter when assessing health risk.

A worked example you can reproduce

Switch to metric units and enter 170 cm, 65 kg, age 30, male, and moderate activity. BMI is 65 ÷ (1.70 × 1.70), or 22.5 after rounding. The tool uses the Mifflin–St Jeor equation by default: for men, 10 × kg + 6.25 × cm − 5 × age + 5; for women, the final term is −161. In this example, estimated resting energy use rounds to 1,568 kcal/day. Moderate activity applies a 1.55 multiplier, so the displayed TDEE is 2,430 kcal/day. These are results of the stated inputs and assumptions, not measured personal needs.

If you enter a body-fat percentage, the tool instead uses the Katch–McArdle equation and an estimated lean mass. That does not make the body-fat input or the output automatically more accurate. Published reviews describe meaningful errors when resting-energy equations are applied to individuals.

What changes when I select another activity level?

The five built-in multipliers are sedentary 1.2, light 1.375, moderate 1.55, active 1.725, and very active 1.9. They are calculation assumptions, not readings from a wearable or a laboratory. Exercise frequency alone may not capture your workday or other movement. If you are unsure which description fits, compare adjacent choices and notice how much the estimate changes. There is no universal rule to subtract a tier to produce a safe diet target.

How to read comparisons without turning them into prescriptions

Does “TDEE − 500” predict a pound of weight loss each week?

No. The ±500-kcal and percentage cards are arithmetic comparisons with an estimatedTDEE. They are not meal plans, weight-change forecasts, or evidence that a particular intake is safe for you. The NIH's body-weight modeling explanation notes that the familiar “3,500 calories per pound” shortcut can overpredict weight loss because metabolism changes as weight changes. If a comparison falls below the estimated resting figure, do not treat it as an intake target; seek individualized advice.

Is the displayed BMI weight band my “ideal weight”?

No. It simply converts the selected BMI category's boundaries into weights at your entered height. The “above/below range” difference is not an instruction to lose or gain that amount. The CDC's BMI FAQ explains that BMI cannot distinguish muscle from fat and should be interpreted alongside other health information. A clinician can put the number in context rather than treating a threshold as a diagnosis.

Are the 50/25/25 macros my nutrition targets?

No. The carbohydrate/protein/fat split and alternate protein-ratio display are examples of how a chosen share of an estimated energy total converts into grams. They do not establish the right diet for a person, activity, or medical condition. The formula's original study and later systematic reviewsupport treating resting-energy output as an estimate with individual limitations. If you are pregnant, breastfeeding, under 20, or managing a health condition, do not use this page to set a diet; discuss your situation with a qualified clinician or dietitian.

Sources: CDC on BMI and its limits, Mifflin–St Jeor original study, systematic review of resting-energy equations, NIH on dynamic body-weight changes. Educational information only; not personal medical advice.