Calculate your BMI with female-specific NHS guidance and ethnicity adjustments
This calculator provides estimates only. Consult your GP or a healthcare professional for personalised advice. BMI is a screening tool and does not account for muscle mass, bone density, or body composition.
Body Mass Index (BMI) is one of the most widely used screening tools for assessing whether someone is within a healthy weight range. While the BMI formula is the same for men and women, the way BMI relates to health risks differs between the sexes. Women naturally carry a higher proportion of body fat than men at the same BMI, and fat distribution patterns in women (particularly after menopause) affect cardiovascular and metabolic risk in ways that BMI alone does not capture. This calculator is designed specifically for women and includes three features that the standard BMI calculator does not: waist circumference risk assessment, ethnicity-adjusted BMI thresholds per NICE clinical guideline CG189, and a combined risk assessment that considers both BMI and waist measurement together. The NHS recommends using waist circumference alongside BMI for a more complete picture of health risk, particularly for women whose waist measures 80 cm or more. For women of South Asian, Chinese, or Middle Eastern heritage, research shows that health risks associated with excess weight begin at a lower BMI than for the general population. NICE guidelines recommend using a BMI of 23 (rather than 25) as the threshold for increased risk, and 27.5 (rather than 30) as the threshold for high risk. This calculator automatically adjusts the categories when you select the relevant ethnicity option.
To use this calculator: 1. Enter your weight in kilograms. If you weigh yourself in stones, multiply by 6.35 to convert. For example, 10 stone 10 pounds = (10 x 6.35) + (10 x 0.454) = 63.5 + 4.5 = 68 kg. 2. Enter your height in metres. For example, 5 foot 5 inches = 1.65 metres. Use the decimal format (e.g. 1.65, not 165 cm). 3. Optionally, enter your waist circumference in centimetres. Measure around your waist at belly button level while standing, breathing normally. Leave at 0 if you do not know. 4. Optionally, select your ethnicity. This adjusts the BMI thresholds per NICE CG189 guidelines. If unsure, leave as "General population." 5. Review your results: - Your BMI value and weight category - Waist circumference risk level (if entered) - Ethnicity-specific guidance (if applicable) - Your healthy weight range for your height - A combined risk assessment considering all factors 6. The bar chart compares your BMI against the healthy range boundaries and overweight threshold.
BMI is calculated using the standard formula: BMI = Weight (kg) / Height (m) squared For example, a woman weighing 68 kg with a height of 1.65 m: BMI = 68 / (1.65 x 1.65) = 68 / 2.7225 = 25.0 Standard NHS categories (general population): - Below 18.5: Underweight - 18.5 to 24.9: Healthy weight - 25.0 to 29.9: Overweight - 30.0 to 34.9: Obese (class 1) - 35.0 to 39.9: Obese (class 2) - 40.0 and above: Obese (class 3) Adjusted thresholds for South Asian, Chinese, and Middle Eastern women (per NICE CG189): - Below 18.5: Underweight - 18.5 to 22.9: Healthy weight - 23.0 to 27.4: Overweight - 27.5 and above: Obese Waist circumference risk levels for women: - Below 80 cm: Low risk - 80 cm to 88 cm: High risk - Above 88 cm: Very high risk The healthy weight range is calculated by working backwards from the BMI thresholds: - Minimum healthy weight = 18.5 x height squared - Maximum healthy weight = 24.9 x height squared (or 23 for South Asian women) The combined risk assessment considers both BMI category and waist circumference together, as recommended by the NHS. When both indicators are elevated, the risk is greater than either alone would suggest.
Inputs: Weight: 68 kg, Height: 1.65 m, Waist: not measured, Ethnicity: General
Inputs: Weight: 62 kg, Height: 1.60 m, Waist: 82 cm, Ethnicity: South Asian
Inputs: Weight: 55 kg, Height: 1.60 m, Waist: 70 cm, Ethnicity: General
BMI is a screening tool and has well-known limitations. It does not distinguish between muscle and fat mass, does not account for age-related changes in body composition, and may not accurately reflect health risk in pregnant or breastfeeding women. If you are pregnant, your midwife will monitor your weight gain using pregnancy-specific guidelines rather than standard BMI categories. After menopause, women tend to accumulate more visceral (abdominal) fat, which increases cardiovascular risk even if BMI remains unchanged. For this reason, waist circumference measurement becomes particularly important for women over 50.