BMI Weight Loss Calculator
Estimate your current BMI, translate a target BMI into a target weight, and see the weight change implied by that target.
Inputs
Required. Decimal point notation only.
Required. Choose kilograms, pounds, or decimal stones.
Required planning value. This tool does not choose a medical target for you.
Live results
BMI band: Overweight
BMI is a screening measure based only on height and weight. It does not directly measure body fat or determine an individual diagnosis.
Current vs. target comparison
| Metric | Current | Target | Difference |
|---|---|---|---|
| BMI | 26.23 | 22.00 | – 4.23 |
| BMI Prime | 1.05 | 0.88 | – 0.17 |
| Weight | 85.0 kg | 71.3 kg | – 13.7 kg |
| BMI band | Overweight | Normal weight | – |
The target column is a mathematical translation of your chosen target BMI at the same height; it is not a personalized medical recommendation.
How to use this BMI weight loss calculator
What this calculator does
This calculator connects three related quantities: height, body weight, and body mass index (BMI). It first calculates your current BMI from height and current weight. Then it translates the Target BMI you enter into a Target weight for the same height. The difference between current and target weight is shown as Change to target. It also reports BMI Prime, which is BMI divided by 25, and a Healthy BMI weight band corresponding to BMI values from 18.5 through 24.9. The tool is intended for adult educational planning. It does not measure body fat, diagnose a condition, or decide which target is appropriate for you.
When to use it
Use the calculator when you want to translate a BMI goal into a body-weight number, compare your current BMI with a target BMI, check how far a chosen target lies from your current weight, or understand the weight range associated with the commonly used adult BMI screening band. BMI is only one screening measure, so it is most useful as context alongside other health information. The NIDDK explains that BMI is based on height and weight and does not directly measure body fat.
How to calculate
- The calculator opens with a ready-to-use example: 180 cm height, 85 kg current weight, and a 22.0 target BMI. The example already has complete results and an immediately available Excel workbook.
- Replace Height with your value. You can switch its unit between centimeters and inches; when you change the unit, the current value is converted rather than simply relabeled.
- Replace Current weight and choose kilograms, pounds, or decimal stones. A value such as 13.5 st means thirteen and a half stones, not thirteen stones plus five pounds.
- Enter a Target BMI. This is a planning input, not a recommendation generated by the calculator. Read the live Target weight, Change to target, target BMI Prime, and comparison table.
- Select Download Excel to export the current validated inputs and results as a real XLSX workbook. Select Reset to clear the demonstration and all user-entered data. After Reset, Excel export is disabled until all required inputs are complete and valid again.
Input guide
Height is required and accepts a positive decimal value from 100 to 250 cm, or the equivalent range in inches. The example is 180 cm. Greater height increases the weight associated with any fixed BMI because height is squared in the formula. Enter a decimal point rather than a decimal comma; ambiguous formats such as “1,80” are rejected instead of being silently reinterpreted. The adjacent Height unit control switches between cm and in and converts the entered height.
Current weight is required and accepts a positive decimal value from 20 to 500 kg, or the equivalent in pounds or stones. The example is 85 kg. At a fixed height, a higher weight produces a higher current BMI and BMI Prime. The Current weight unit selector changes among kg, lb, and st and converts the current entry. Do not paste unit letters, thousands separators, scientific notation, or a stones-and-pounds phrase into the numeric box; use the unit selector instead.
Target BMI is required and accepts a decimal value from 10 to 60. The example is 22.0. A higher target BMI produces a higher target weight; a lower target BMI produces a lower target weight. The calculator deliberately allows values outside the commonly used adult healthy band so you can inspect scenarios, but that does not make every scenario medically appropriate. For individual goals, discuss relevant medical history, body composition, medicines, pregnancy status, or other factors with a qualified health professional.
Output guide
Current BMI is weight in kilograms divided by height in meters squared. BMI band places that value into the calculator's simplified BMI bands. BMI Prime is current BMI divided by 25, so 1.00 corresponds to BMI 25. Target BMI repeats the planning value you entered, while Target BMI Prime is that target divided by 25. Target weight is the body weight that mathematically corresponds to the target BMI at the same height. Change to target says Lose, Gain, or Maintain and reports the absolute weight difference in your selected weight unit. Healthy BMI weight band converts BMI 18.5 – 24.9 into a weight interval for your height. The summary pills repeat current BMI, BMI band, target weight, and change direction so the main state remains easy to scan.
The Current vs. target comparison table contains four rows: BMI, BMI Prime, Weight, and BMI band. The Current and Target columns are driven by the same canonical calculation as the result cards. Difference is target minus current; a negative weight difference means the target is lighter, while a positive difference means it is heavier. A zero difference means the current and target values coincide.
Worked example
With the startup example, height is 180 cm, which is 1.80 m, and current weight is 85 kg. Current BMI is 85 ÷ (1.80 × 1.80) = 26.23. BMI Prime is 26.23 ÷ 25 = 1.05. For a target BMI of 22.0, target weight is 22.0 × (1.80 × 1.80) = 71.28 kg, displayed as 71.3 kg. The weight difference is 71.28 – 85 = – 13.72 kg, so Change to target displays Lose 13.7 kg. The weight interval corresponding to BMI 18.5 – 24.9 at 1.80 m is about 59.9 – 80.7 kg. These figures are mathematical BMI translations, not a prescription.
Learn more
For adult BMI categories and their role as a screening measure, see the National Heart, Lung, and Blood Institute guidance on adult BMI categories. For broader weight-management planning that considers time, calorie intake, and physical activity rather than BMI alone, the NIDDK Body Weight Planner provides a more detailed modeling approach.
How the BMI and target-weight math works
The core equation is simple: BMI = weight in kilograms ÷ height in meters². Rearranging that identity gives target weight = target BMI × height in meters². Because the same height is used on both sides of the comparison, the difference between current and target weight follows directly from those two quantities. No calorie deficit, time-to-goal, metabolic adaptation, fluid change, or body-composition model is included.
BMI = weight(kg) / height(m)² | target weight(kg) = target BMI × height(m)² | BMI Prime = BMI / 25
Interpreting BMI carefully
Adult BMI is widely used because it is fast and reproducible, but it is a screening metric rather than a direct measure of fat mass. A very muscular person can have a high BMI with comparatively low body fat, while two people with the same BMI may have different body composition or health risks. The NIDDK's explanation of BMI and waist size describes several situations where BMI alone may not reflect individual risk well.
The calculator's healthy weight band is therefore best read as the weight interval corresponding mathematically to BMI 18.5 – 24.9, not as a guarantee that every weight in that band is ideal for every person. Children and teenagers require age- and sex-specific growth-chart interpretation rather than the adult thresholds used here. Pregnancy also changes how body weight should be interpreted. If you have a health condition, take medicines that affect weight, have a history of disordered eating, are pregnant, or are considering a substantial weight change, individualized professional guidance is more appropriate than relying on this calculator alone.
Planning beyond a single target number
A target weight does not say how quickly weight should change or what actions are appropriate. Sustainable weight management typically involves dietary patterns, physical activity, sleep, health conditions, medicines, and long-term habits. For a model that explicitly includes calorie and activity changes over time, use the NIDDK planner linked above. Treat the BMI target here as a transparent mathematical scenario that helps you ask better questions, not as a substitute for clinical assessment.