BMI Prime Calculator
Calculate adult BMI Prime (BMI divided by 25), BMI and category, with the weight interval for BMI 18.5 to less than 25 at your height.
BMI Prime is BMI divided by 25, the threshold at which the CDC adult overweight category begins. A value of 1.20 means BMI is 20% above that threshold; 0.90 means it is 10% below. This calculator is for adults aged 20 or older and provides a screening comparison, not a diagnosis or an individual weight prescription.
How to use this tool
- Enter your weight and choose kilograms or pounds.
- Enter your height and choose centimeters or inches (5 ft 9 in = 69 in).
- Read your BMI Prime, BMI and category.
- Use the table to see the weight range for each category at your height.
Formula
BMI Prime = BMI ÷ 25, where BMI = weight (kg) ÷ height (m)²
BMI Prime has no units. The healthy BMI range of 18.5 to <25 becomes 0.74 to <1, overweight is 1 to <1.2 and obesity starts at 1.20. Pounds and inches are converted exactly (1 lb = 0.45359237 kg, 1 in = 2.54 cm) rather than with the rounded 703 factor, so results can differ from some charts in the second decimal.
Example
At 70 kg and 175 cm, BMI = 70 ÷ 1.75² = 22.857, and BMI Prime = 22.857 ÷ 25 = 0.9143. The BMI 25 threshold is 25 × 1.75² = 76.5625 kg. The healthy-weight screening interval starts at 56.65625 kg and excludes 76.5625 kg; the displayed endpoints are rounded.
Frequently asked questions
What is a good BMI Prime?
A value from 0.74 to less than 1.00 matches the CDC adult healthy-weight BMI category. Exactly 1.00 is the overweight threshold. Classification uses unrounded BMI even when the displayed number rounds to a boundary.
How do I read a BMI Prime of 1.3?
Your BMI is 30% above 25 — a BMI of 32.5, which is obesity class 1. Because BMI scales directly with weight at a fixed height, reaching 1.00 would mean weighing about 1 ÷ 1.3 ≈ 77% of your current weight.
Does BMI Prime work for children, athletes or older adults?
It shares the limits of BMI. Children need age- and sex-specific percentiles, muscular people can score high without excess fat, and some Asian populations face higher health risk at lower BMIs, which is why several countries use 23 as the overweight cut-off.
Sources
- CDC — Adult BMI Categories
- WHO — Obesity and overweight fact sheet
- Gadzik J. "How much should I weigh?" — Quetelet's equation, upper weight limits, and BMI prime. Conn Med 2006;70(2):81–88
This tool gives an estimate for general information only. It is not financial, tax, legal or medical advice — check with a qualified professional before you rely on the result.
Last updated: 2026-10-30