Your optimal weight isn’t a single number. It’s a range that depends on your height, age, sex, muscle mass, and where your body stores fat. The most common starting point is BMI (body mass index), which puts a “healthy weight” between 18.5 and 24.9 for adults, but that range has real limitations. A better answer comes from combining several simple measurements that together paint a more accurate picture of your health.
What BMI Tells You (and What It Doesn’t)
BMI divides your weight in kilograms by your height in meters squared. The CDC defines the categories for adults 20 and older like this:
- Underweight: below 18.5
- Healthy weight: 18.5 to 24.9
- Overweight: 25 to 29.9
- Obesity: 30 or higher
For a 5’8″ person, the healthy BMI range translates to roughly 125 to 163 pounds. That’s a 38-pound spread, which shows how much individual variation exists even within a single height. Your “optimal” spot in that range depends on your frame size, muscle mass, and personal health markers.
BMI’s biggest flaw is that it can’t tell the difference between fat and muscle. A muscular athlete with low body fat can easily land in the “overweight” category. Research on young male athletes found that the standard BMI cutoff of 25 misclassified many of them as overweight when body scans showed they were lean. More accurate cutoffs for athletic men turned out to be 28.2 for overweight and 33.7 for obesity. If you carry significant muscle, BMI will overestimate your risk.
A Quick Formula to Estimate Your Target
Clinicians sometimes use simple height-based formulas to estimate an ideal body weight. The most widely cited ones work like this for anyone 5 feet (60 inches) or taller:
- Men: Start at 106 pounds for 5 feet, then add 6 pounds for each additional inch of height.
- Women: Start at 100 pounds for 5 feet, then add 5 pounds for each additional inch.
So a 5’6″ woman would get an estimate of about 130 pounds, and a 5’10” man would land around 166 pounds. These formulas are rough guides, not prescriptions. They were designed for medication dosing, not lifestyle goals, and they don’t account for age, ethnicity, or body composition. Think of them as a midpoint to orient yourself, not a target to hit exactly.
Why Waist Size Matters More Than Scale Weight
Where you carry fat is often more important than how much you weigh. Fat stored deep in the abdomen, called visceral fat, wraps around your organs and drives up the risk of heart disease, type 2 diabetes, and metabolic problems. You can be at a “normal” weight and still carry too much visceral fat, or be technically overweight with most of your fat stored harmlessly under the skin.
Two easy measurements help you assess this:
- Waist-to-height ratio: Your waist circumference should be less than half your height. If you’re 5’8″ (68 inches), your waist should stay under 34 inches. The NHS recommends this as a simple screening tool, and research links ratios above 0.5 to higher risk of circulatory and metabolic disease.
- Waist circumference alone: A waist of 35 inches or more in women, or 40 inches or more in men, signals elevated health risk from abdominal fat, according to the Cleveland Clinic.
To measure your waist accurately, wrap a tape measure around your bare midsection at the level of your belly button, standing relaxed without sucking in. Do it first thing in the morning for the most consistent reading.
Body Fat Percentage: A More Precise Measure
If you want a clearer picture than BMI or waist measurements, body fat percentage gets closer to the truth. There’s no universally agreed-upon “ideal” range, but a large 2025 study using U.S. national survey data defined the thresholds this way: overweight starts at 25% body fat for men and 36% for women, while obesity starts at 30% for men and 42% for women.
Women naturally carry more essential fat than men, which is why their healthy ranges are higher. For general fitness (not competitive athletics), most guidelines place a healthy range at roughly 14 to 24% for men and 21 to 35% for women, though these shift upward somewhat with age.
Getting an accurate body fat reading usually requires more than a bathroom scale. DEXA scans (a type of low-dose X-ray) are considered the gold standard. Many gyms and clinics offer them for a modest fee. Bioelectrical impedance scales you can buy for home use give a ballpark estimate but can swing by several percentage points depending on hydration, meal timing, and the device itself.
Your Optimal Weight Changes With Age
The “ideal” BMI range of 18.5 to 24.9 was developed primarily from data on younger and middle-aged adults. For people over 65, the picture shifts. A study tracking elderly men and women in Norway found that those with a BMI of 25 to 29.9, technically in the “overweight” category, had the lowest mortality rates. Moderately obese women also showed relatively low mortality in this age group.
Several things explain this pattern. Being underweight in older age is linked to loss of both limb and respiratory muscle, weakened immune function, and greater vulnerability to acute illness. Carrying a modest amount of extra weight appears to provide a buffer during serious illness or surgery. Meanwhile, the health consequences of excess weight develop slowly, and in older adults with shorter remaining life expectancy, the risks of moderate overweight may never fully materialize.
This doesn’t mean weight gain is protective. It means that for older adults, aggressively pursuing a BMI under 25 may do more harm than good, especially if it comes at the expense of muscle mass. Maintaining strength and staying physically active matters more than chasing a number on the scale.
How to Find Your Personal Number
Rather than fixating on one metric, use several together to triangulate your optimal range:
- Calculate your BMI to see where you fall in the broad population categories. If you’re between 18.5 and 24.9 and don’t carry much muscle, it’s a reasonable starting point.
- Measure your waist-to-height ratio. If it’s under 0.5, your abdominal fat is likely in a healthy range regardless of what the scale says.
- Consider your body fat percentage if BMI seems misleading for your body type, especially if you’re muscular or very lean.
- Factor in your age. If you’re over 65, a BMI in the low-to-mid overweight range may actually be your healthiest zone.
Your optimal weight is also the weight where your blood pressure, blood sugar, cholesterol, and energy levels are in good shape, where you sleep well and can do the physical activities you care about. Two people of the same height and age can thrive at meaningfully different weights. The most useful question isn’t “what should I weigh?” but “what weight lets my body function at its best?”