What Is a Normal BMI for My Age and Height

A normal BMI for adults is between 18.5 and 24.9, regardless of age. The healthy range does not change as you get older — a 25-year-old and a 60-year-old use the same BMI thresholds. What changes with age is how your body composition shifts inside that range, which is why BMI alone tells an incomplete story after 65.

BMI (Body Mass Index) is the most widely used screening tool for weight classification. According to the CDC, approximately 73.6% of American adults fall in the overweight or obese BMI categories. The number matters not because it defines your health, but because it is the first filter clinicians use to identify elevated risk for conditions like type 2 diabetes, hypertension, and cardiovascular disease.

Use the free BMI Calculator at RoughTools to find your BMI instantly — or follow the step-by-step method below.

The Body Mass Index Formula

BMI is calculated the same way for every adult. There are two versions: metric and imperial.

Metric formula:

BMI = weight (kg) / height (m)²

Imperial formula:

BMI = (weight in lbs × 703) / height in inches²

Where:

Weight — your current body weight in kilograms or pounds
Height — your height in meters (metric) or inches (imperial)
703 — a unit conversion constant that makes the imperial formula equivalent to metric
BMI — a unitless number; the result places you in one of four weight categories

Worked example: 35-year-old woman, 5'6", 148 lbs

Step 1 — Convert height to inches:

5'6" = (5 × 12) + 6 = 66 inches

Step 2 — Apply the imperial BMI formula:

BMI = (148 × 703) / 66²
BMI = 104,044 / 4,356
BMI = 23.9

The result: a BMI of 23.9 places this woman in the Normal weight category (18.5–24.9). She is well within the healthy range, closer to the upper boundary than the lower one — a common and unremarkable finding for an average-height adult woman in her mid-thirties.

Note: metric calculation gives the identical result. 148 lbs ÷ 2.205 = 67.1 kg; 66 inches × 0.0254 = 1.676 m. BMI = 67.1 ÷ (1.676)² = 67.1 ÷ 2.809 = 23.9. Both formulas are mathematically equivalent.

How to Calculate Your BMI Step by Step

Measure your current weight. Use a scale that shows weight in pounds or kilograms. Weigh yourself in the morning before eating, with minimal clothing, for the most consistent result. Do not use a goal weight — BMI is a measure of where you are now, not where you want to be.
Measure your height accurately. Stand against a flat wall without shoes. Place a flat object (a book works well) on top of your head, mark the wall, then measure from the floor to the mark. People commonly overestimate their height by 0.5–1 inch, which can shift BMI by 0.3–0.5 points.
Convert units if using imperial measurements. Convert height to total inches (feet × 12 + remaining inches) and square it. For 5'9": (5 × 12) + 9 = 69 inches. 69² = 4,761.
Apply the formula. Multiply your weight in pounds by 703, then divide by your height in inches squared. On a calculator: (weight × 703) ÷ (height in inches)². For a 185-pound person at 5'9": (185 × 703) ÷ 4,761 = 130,055 ÷ 4,761 = 27.3.
Look up your category. Compare your result to the four standard BMI categories: under 18.5 is underweight, 18.5–24.9 is normal, 25.0–29.9 is overweight, 30.0 and above is obese. The example BMI of 27.3 lands in the overweight range.
Verify the result is plausible. A sanity check: for most adults of average height (5'4"–5'10"), a normal BMI corresponds to a weight range of roughly 110–185 pounds. If your BMI result places you far outside what seems realistic given your build, recheck that you used total inches (not feet and inches separately) for height.

Pro tip: BMI is calculated the same way regardless of age for adults 20 and older. The formula does not include an age variable. If a website asks for your age to calculate adult BMI, it is either calculating something beyond standard BMI or adding unnecessary steps.

What Is a Healthy BMI Range by Age?

For adults 20 and older, the healthy BMI range is 18.5–24.9 at every age. The CDC and WHO both use the same four categories regardless of whether you are 22 or 72.

The table looks the same across age groups because BMI is a weight-to-height ratio — not a developmental measure. Age-adjusted BMI only applies to children and teenagers (ages 2–19), where the calculation uses sex- and age-specific growth percentiles instead of fixed category cutoffs.

| BMI | Weight category | |---|---| | Below 18.5 | Underweight | | 18.5 – 24.9 | Normal (healthy) weight | | 25.0 – 29.9 | Overweight | | 30.0 and above | Obese |

That said, research published in the American Journal of Clinical Nutrition notes that older adults (65+) with a BMI in the 25–27 range may actually have lower mortality risk than those at the lower end of the normal range. Muscle mass decreases with age, so a slightly higher BMI in older adults may reflect preserved muscle, not excess fat. This is why BMI is less reliable as a sole metric after 65 — body composition matters more.

For a more precise picture at any age, the body fat calculator estimates body fat percentage, which does not have the same age-related interpretation limits that BMI does.

What BMI Is Considered Overweight or Obese?

A BMI of 25.0 or above is classified as overweight; a BMI of 30.0 or above is classified as obese. These thresholds are set by the World Health Organization and adopted by the CDC, and they apply to adults of all ages.

Here is how the categories break down with specific weight examples for a person who is 5'8" (68 inches):

| BMI range | Category | Weight range at 5'8" | |---|---|---| | Below 18.5 | Underweight | Below 122 lbs | | 18.5 – 24.9 | Normal | 122 – 163 lbs | | 25.0 – 29.9 | Overweight | 164 – 196 lbs | | 30.0 – 34.9 | Obese (Class I) | 197 – 229 lbs | | 35.0 – 39.9 | Obese (Class II) | 230 – 262 lbs | | 40.0 and above | Obese (Class III) | 263 lbs and above |

One important nuance: the overweight category does not automatically indicate a health problem. Highly muscular people — athletes, weightlifters — frequently have BMIs in the 25–30 range despite low body fat, because muscle weighs more than fat at the same volume. BMI cannot distinguish between muscle weight and fat weight. A 200-pound man at 5'10" with 12% body fat and a 200-pound man at 5'10" with 32% body fat have identical BMIs of 28.7, but very different health profiles.

If your BMI is in the overweight range and you exercise regularly with substantial muscle, use the body fat calculator alongside your BMI result.

What Is a Normal BMI for Women vs Men?

The standard BMI formula is identical for men and women — the same weight and height inputs, the same category thresholds. There is no separate normal BMI range for women vs men at the same BMI value.

However, the same BMI number represents different body fat percentages in men and women. Women naturally carry more essential body fat than men (approximately 10–13% for essential fat in women vs 2–5% in men), which means a woman and a man with identical BMIs of 22 will have different body fat percentages — the woman's will typically be higher by 5–7 percentage points.

This is not a flaw in BMI for women — the healthy BMI range accounts for this difference by design. A BMI of 22 is healthy for both a woman and a man, even though their absolute fat percentages differ. The category boundaries are population-calibrated to reflect healthy outcomes for both sexes at each BMI level.

Where sex becomes important is in waist circumference health thresholds. According to the National Heart, Lung, and Blood Institute (NHLBI), a waist circumference above 35 inches in women (vs 40 inches in men) indicates elevated cardiometabolic risk at the same BMI. The waist-to-hip ratio calculator combines waist and hip measurements for a more sex-sensitive fat distribution assessment.

Common Mistakes to Avoid When Calculating BMI

Using height in feet-and-inches without converting to total inches. Entering 5.6 instead of 66 inches is the most common arithmetic error. The formula requires total inches (66), not decimal feet (5.6). 5.6² = 31.4; 66² = 4,356 — a factor of 138 difference that produces a completely wrong result.
Using the wrong formula for the unit system. The metric formula (kg/m²) does not work with pounds and inches. Mixing units without the 703 conversion constant gives a BMI result roughly 4.5 times too low. Always confirm which unit system you are using before starting.
Assuming BMI determines health directly. BMI is a screening tool, not a diagnosis. A BMI of 27 does not mean someone is unhealthy, and a BMI of 22 does not mean someone is healthy. BMI is most useful when considered alongside blood pressure, blood glucose, waist circumference, and activity level — not in isolation.
Using the adult formula for children under 20. Children's and teenagers' BMI uses the same calculation, but the result is interpreted differently — compared against sex- and age-specific growth percentiles, not the adult categories above. A BMI of 22 in a 14-year-old is interpreted as "85th percentile for age and sex," not simply "normal." The CDC provides separate BMI-for-age charts for ages 2–19.
Rounding height down to the nearest inch. A person who is 5'6.5" and rounds down to 5'6" introduces a BMI error of approximately 0.2. That seems small, but it can shift a result from 24.8 (normal) to 25.0 (overweight), which matters in a clinical setting. Measure height precisely.

Frequently Asked Questions

What is considered a healthy BMI? A healthy BMI for adults is 18.5 to 24.9. This range applies to all adults 20 and older regardless of age or sex. On a practical level, for a person who is 5'7" (67 inches), a healthy weight corresponds to 118–159 pounds. For 5'10", the healthy weight range is 129–173 pounds. Use the BMI calculator to find the specific weight range that falls within the healthy zone for your exact height.

What if my BMI says I'm overweight but I feel healthy and exercise regularly? BMI cannot distinguish between fat mass and muscle mass. Athletes and people with high muscle mass frequently have BMIs in the overweight range (25–29.9) despite low body fat percentages. If you are physically active and your weight is largely muscle, your BMI overestimates your health risk. In this case, a body fat percentage measurement — via DEXA scan, hydrostatic weighing, or a validated estimation formula — gives a more accurate picture than BMI alone. A BMI of 27 with 15% body fat is a very different health scenario than a BMI of 27 with 32% body fat.

What is the difference between BMI and body fat percentage? BMI is a ratio of weight to height squared — it uses only two inputs and takes five seconds to calculate. Body fat percentage is the proportion of your total body weight that is fat tissue. BMI is a population-level screening tool; body fat percentage is an individual health metric. The two are correlated but not interchangeable. A BMI of 30 typically corresponds to a body fat percentage of around 30–38% in women and 24–32% in men, but the ranges overlap widely. For most general health screening purposes, BMI is sufficient. For body composition goals (building muscle, reducing fat), body fat percentage is the more useful number.

How much do I need to weigh to reach a normal BMI? For a BMI of exactly 24.9 (the top of the normal range), multiply 24.9 by your height in meters squared. For 5'6" (1.676 m): 24.9 × (1.676)² = 24.9 × 2.809 = 69.9 kg = 154 lbs. For 5'10" (1.778 m): 24.9 × (1.778)² = 24.9 × 3.161 = 78.7 kg = 174 lbs. These are the maximum weights for a normal BMI at each height. For the lower boundary (BMI 18.5), use 18.5 in place of 24.9.

When should I be concerned about my BMI? A BMI below 17.5 or above 35 warrants a conversation with your doctor regardless of other factors. Between 17.5–18.5 (underweight) or 30–35 (Class I obese), the appropriate response depends heavily on context — your age, activity level, existing health conditions, and whether the BMI is trending up or down over time. A one-time BMI reading matters less than the trajectory. A person who was BMI 32 twelve months ago and is now 28 is moving in a healthy direction even though they are still in the overweight range. Consult your doctor before making significant dietary or exercise changes based on BMI alone, especially if you have existing medical conditions.

Use the Free BMI Calculator

The Free BMI Calculator at RoughTools calculates your BMI using the standard WHO formula and instantly shows your weight category, your healthy weight range for your height, and how many pounds you are above or below the normal range boundary. It works in both metric and imperial units and does not require unit conversion on your part. No account needed, no data stored, completely free.

Free BMI Calculator →

You might also need:

Calorie Calculator — calculate your daily calorie target to reach a healthy BMI
Body Fat Calculator — estimate body fat percentage for a more complete picture than BMI
Ideal Weight Calculator — find your target weight range using multiple established formulas
Waist-Hip Ratio Calculator — assess fat distribution risk, especially relevant above BMI 25