Calorie Calculator

Basal metabolic rate: An estimate of how much energy your body uses at rest for basic functions like breathing and circulation.

Maintenance calories: Your estimated total daily energy use after your activity level is applied. This is often called TDEE.

Daily calorie target: The intake estimate for your selected Goal. It matches maintenance for maintain, goes below for loss, and above for gain.

Daily calorie change from maintenance: The amount added to or subtracted from maintenance calories. A negative number means a deficit. A positive number means a surplus.

Weekly pace (selected unit): The planned amount of weight to lose or gain each week, entered in lb/week or kg/week.

BMR equation: The formula used to estimate resting energy needs. This calculator offers Mifflin-St Jeor, Revised Harris-Benedict, and Katch-McArdle.

Body fat (%): The percent of your body weight that is fat. It is only needed when using Katch-McArdle.

Estimated time to target: The number of weeks it would take to reach Target weight (selected unit) if your weekly pace stays the same.

Mistake: Entering Age (years) under 18.
Fix: Use this calculator only for adults 18 and older, and enter a whole-number adult age in Age (years).

Mistake: Mixing Height unit with the wrong height fields, such as choosing Centimeters but filling Height (ft) and Height (in).
Fix: Match Height unit to the field you complete: use Height (ft) and Height (in) for feet and inches, or use Height (cm) for metric.

Mistake: Entering inches over 11 in Height (in).
Fix: Keep Height (in) from 0 up to but not including 12, and put the rest in Height (ft).

Mistake: Choosing Lose weight or Gain weight but leaving Weekly pace (selected unit) blank or at 0.
Fix: Enter a positive Weekly pace (selected unit). The Daily calorie target cannot be calculated for a change goal without it.

Mistake: Entering a Target weight (selected unit) that does not match the Goal.
Fix: For Lose weight, Target weight (selected unit) should be below Current weight (selected unit). For Gain weight, it should be above.

Mistake: Selecting Katch-McArdle without entering Body fat (%).
Fix: If BMR equation is Katch-McArdle, enter Body fat (%) greater than 0 and less than 100, or switch to Mifflin-St Jeor or Revised Harris-Benedict.

• This calculator is for adults 18 and older and blocks younger ages.
• Results are estimates, not direct measurements. Real calorie needs can differ because metabolism, activity, and body changes are not perfectly constant.
• Maintenance calories are based on a selected activity factor, so choosing the wrong Activity level can shift the result a lot.
• The weight-change plan uses the simple 3,500 kcal per pound planning rule, which is a rough shortcut and becomes less accurate over time.
• Katch-McArdle depends on Body fat (%). If that input is off, the BMR result can also be off.
• Estimated time to target appears only when Target weight (selected unit) matches the selected Goal direction and Weekly pace (selected unit) is positive.
• If Daily calorie target falls below 1,000 kcal/day, the tool flags the plan as too low for this simple calculator instead of treating it as a normal target.
• Unit choices matter: Current weight (selected unit), Target weight (selected unit), and Weekly pace (selected unit) must match their selected units for correct results.

Calculation steps

The calculator first converts your height and weight into metric units when needed. Feet and inches are converted to centimeters, and pounds are converted to kilograms.

height_cm = (height_ft x 12 + height_in) x 2.54

weight_kg = weight_lb x 0.45359237

Next, it estimates Basal metabolic rate using the selected BMR equation.

Mifflin-St Jeor, male: BMR = 10 x weight_kg + 6.25 x height_cm - 5 x age_years + 5

Mifflin-St Jeor, female: BMR = 10 x weight_kg + 6.25 x height_cm - 5 x age_years - 161

Revised Harris-Benedict, male: BMR = 88.362 + 13.397 x weight_kg + 4.799 x height_cm - 5.677 x age_years

Revised Harris-Benedict, female: BMR = 447.593 + 9.247 x weight_kg + 3.098 x height_cm - 4.330 x age_years

Katch-McArdle: lean_mass_kg = weight_kg x (1 - body_fat_pct / 100)

Katch-McArdle: BMR = 370 + 21.6 x lean_mass_kg

Maintenance calories are then estimated by multiplying BMR by the selected activity factor. The activity factors are 1.2, 1.375, 1.55, 1.725, and 1.9.

TDEE = BMR x activity_factor

For weight loss or gain, the calculator converts your requested weekly pace into a daily calorie change using the simple planning rule of 3,500 kcal per pound. Loss uses a negative change, and gain uses a positive change.

weekly_change_lb = weekly_change_kg x 2.2046226218

daily_adjustment_kcal = weekly_change_lb x 3500 / 7

daily_target = TDEE + signed_daily_adjustment_kcal

If you enter a target weight that matches your goal direction, the calculator estimates time by dividing the total weight change by the weekly pace in the same unit.

time_to_target_weeks = abs(target_weight - current_weight) / weekly_change_in_same_unit

If Energy unit is set to kJ, outputs are converted after all kcal-based math is complete.

kJ = kcal x 4.184

Mini example

A 40-year-old male who is 5 ft 10 in, weighs 200 lb, chooses Light activity, and wants to lose 1 lb per week with Mifflin-St Jeor gets a BMR of about 1,853 kcal/day and maintenance calories of about 2,548 kcal/day. A 1 lb per week loss uses a 500 kcal/day deficit, so the daily calorie target is about 2,048 kcal/day. If the target weight is 180 lb, the estimated time is 20 weeks.

Interpretation

Basal metabolic rate is your resting estimate. Maintenance calories are your starting point for keeping weight about the same. Daily calorie target shows the intake linked to your selected plan. A larger negative Daily calorie change from maintenance means a more aggressive deficit, while a larger positive value means a more aggressive surplus.

Assumptions used

The tool assumes your weekly pace stays steady, your activity level stays similar over time, and your body responds in a roughly linear way. In real life, calorie needs can change as body weight, activity, and adherence change [2]. If the result falls below 1,000 kcal/day, the calculator shows a strong warning because that intake is too low for this simple planning tool [1].