Health · 4 min read

Ideal Weight for Height and Age: What Actually Changes

Written by Muhammad Ajmal · Last reviewed 2026-07-29

The formulas used to calculate ideal weight - Devine, Robinson, Miller, and Hamwi - all work from a single input: height. None of them ask for your age, which surprises a lot of people searching for an ideal weight tied to both height and age. The short answer is that these formulas don't adjust for age at all, but that doesn't mean age is irrelevant to the picture.

What the height-based formulas actually give you

Each formula assigns a base weight for 5 feet of height, then adds a fixed amount per inch above that. The Devine formula, originally built for drug dosing calculations, sets a base of 50 kg for men and 45.5 kg for women, then adds 2.3 kg per inch over 5 feet. Robinson and Miller use slightly different constants but follow the same structure. Run your height through the calculator and you get a single target weight or a narrow range, with no age field to fill in.

Why age changes the context, not the formula

Body composition shifts over a lifetime even when the number on the scale stays flat. Muscle tends to make up a smaller share of body weight as people move through their 30s, 40s, and beyond, while fat tends to make up a larger share, often without much change in total weight. Two people at the same height and the same "ideal" weight from a formula can have quite different amounts of muscle and fat depending on their age and activity level. The formula can't see any of that. It only sees height.

BMI ranges stay the same across adult ages

The standard healthy BMI band of 18.5 to 24.9 applies to all adults from 18 to over 65, with no official age adjustment in most guidelines. Some clinicians note that mild extra weight in older adults is not tied to the same risks as it is in younger adults, since it can act as a buffer during illness later in life. That's a clinical judgment call for an individual case, not a change to the standard formula.

What matters more than the number as you age

Maintaining muscle mass through resistance exercise and adequate protein intake matters more with each passing decade, since muscle loss is a normal part of aging that accelerates without deliberate effort to counter it. A person who keeps their weight in the healthy range but loses muscle over the years is not in the same physical condition as someone who stays at a similar weight while maintaining strength. Weight alone, whether "ideal" by formula or not, cannot show that difference.

A practical way to use ideal weight by decade

Rather than looking for a different formula at each age, check your number periodically and pay attention to what's changing around it. Someone in their 20s hitting their ideal weight target with little exercise and someone in their 50s hitting the same number after years of strength training are in very different places physically, even though the calculator gives them the same answer. Use the ideal weight calculator as a starting reference point, then track body composition, energy levels, and strength over time rather than chasing the number itself.

When the formula matters less

Ideal weight formulas were designed for population averages and medical dosing, not for judging any one person's health. Athletes, pregnant women, and anyone with an unusually high or low muscle mass for their height will often fall outside the formula's range while being perfectly healthy. Age is one more reason the number is a starting point rather than a verdict.

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