How this tool works
Body mass index (BMI) compares your weight with your height. It is a quick screening number, not a measure of health on its own. This calculator uses the standard formula and the adult categories published by the Centers for Disease Control and Prevention (CDC).
You enter your height in feet and inches and your weight in pounds. The tool first turns your height into inches (feet × 12, plus the extra inches). It then applies the formula:
BMI = weight in pounds ÷ (height in inches × height in inches) × 703
The result is matched to a CDC category:
| BMI | CDC category |
|---|---|
| Under 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25–29.9 | Overweight |
| 30 or higher | Obesity |
The tool also works the formula backward to show the weight range that would give a BMI of 18.5 to 24.9 at your height. That range is the "healthy weight" band in the CDC table, shown in pounds so it is easier to picture.
A worked example
Take a person who is 5 feet 7 inches tall and weighs 170 pounds.
- Height in inches: 5 × 12 + 7 = 67 inches
- Height squared: 67 × 67 = 4,489
- 170 ÷ 4,489 × 703 = about 26.6
A BMI of 26.6 falls in the overweight category. The weight range for a BMI of 18.5 to 24.9 at 67 inches is:
- Low end: 18.5 × 4,489 ÷ 703 = about 118 pounds
- High end: 24.9 × 4,489 ÷ 703 = about 159 pounds
So the tool would show a range of roughly 118 to 159 pounds for this height.
Limits of this tool
BMI has real limits, and they matter more as we age. It does not measure muscle, and it does not show where fat is stored. Many people lose muscle as they get older, and that loss can hide extra fat, so a "healthy" BMI does not always mean a healthy body makeup. Some research suggests the lowest-risk BMI for older adults may be a little higher than the standard range, but the right target for you is something your doctor should set. Read more in our guide to BMI for older adults.
When to talk to your doctor
Call your doctor if you are losing weight without trying. Unintended weight loss in older adults deserves attention, whatever your BMI. It is also worth a conversation if your BMI is in the underweight or obesity range, or if your weight has changed a lot in a short time. Eating enough protein can help protect muscle; our protein calculator shows a daily range based on your weight.
Frequently asked questions
Is BMI accurate for people over 65?
It is a useful starting point but an imperfect one. Because it cannot tell muscle from fat, it can miss changes that come with age. Your doctor may look at other things, such as waist size, strength and recent weight changes.
Why does the formula multiply by 703?
BMI was designed with kilograms and meters. Multiplying by 703 converts the result when you use pounds and inches, so you get the same number either way.
Should I try to reach the middle of the weight range?
Not necessarily. The range is a general guide for adults. Your doctor can tell you whether a different target makes more sense for your health and history.
Does Medicare cover help with weight?
Medicare Part B covers obesity counseling for people with a BMI of 30 or higher, and nutrition therapy for people with diabetes or kidney disease. Ask your doctor whether you qualify.
Sources
Want the full picture? Read our guide: BMI for Older Adults: What It Shows, What It Misses.
Read the guideThis tool gives general information for education only. It does not diagnose any condition or replace advice from your doctor, nurse or pharmacist. In an emergency call 911. See our medical disclaimer and sources.