The Monthly Body Mass Index Calculator compares BMI at the beginning and end of a monthly tracking period using one height and two body weights. It reports the ending BMI, the BMI change, and the corresponding weight change in either metric or US customary units.
BMI is a screening ratio based only on weight and height; it does not directly measure body fat, muscle mass, fat distribution, or health. The calculator can help keep a consistent monthly record, but the result should be interpreted alongside other information and professional guidance when health decisions are involved.
1. Choose a measurement system
Select metric for kilograms and centimeters or US customary for pounds and inches.
2. Enter height
Use the same adult height for both BMI calculations.
3. Enter starting weight
Add the weight recorded at the beginning of the monthly period.
4. Enter ending weight
Add the weight recorded at the end of the period in the same unit.
5. Review the change
The main result is ending BMI, while the breakdown shows starting BMI and the difference.
For metric entries, height in centimeters is divided by 100 before squaring. The calculation assumes height is unchanged during the period.
The ending BMI is the weight-to-height ratio calculated from the final weight; the change indicates how that ratio moved during the selected month.
BMI is a screening measure and may not represent body composition or health risk accurately for every individual.
Given: Height 175 cm, starting weight 82 kg, and ending weight 80.5 kg.
Calculation: Height = 1.75 m. Starting BMI = 82 ÷ 1.75² = 26.7755. Ending BMI = 80.5 ÷ 1.75² = 26.2857. BMI change = 26.2857 − 26.7755 = −0.4898.
Result: Ending BMI 26.29, a BMI change of about −0.49, and a weight change of −1.5 kg.
No. BMI is calculated only from weight and height and cannot distinguish fat mass from lean mass.
No. Select one measurement system and enter all values in the units shown for that system.
Height is fixed in the formula, so BMI changes directly in proportion to weight.
No. Health assessment may also consider medical history, waist measures, body composition, laboratory data, symptoms, and other factors.
BMI uses only height and weight, while a body-fat calculator estimates the proportion of body weight that is fat using a separate measurement method.