Ideal Body Weight vs. Goal Weight: What's the Difference?

What Is Ideal Body Weight?

Ideal Body Weight (IBW) is a medical estimate of a healthy weight for a given height, developed primarily for medication dosing and clinical reference. Common formulas include Hamwi (1964) and Devine (1974). They were developed from population data and produce similar results.

Hamwi Formula

Men: 106 lbs for first 5 feet + 6 lbs per inch over 5 feet
Women: 100 lbs for first 5 feet + 5 lbs per inch over 5 feet
Example: 5'10" male = 106 + (10 × 6) = 166 lbs IBW

IBW doesn't account for frame size or muscle mass — a muscular 5'10" man would legitimately be well above 166 lbs without excess fat.

Goal Weight: A Better Personal Target

Goal weight is what you want to weigh based on your personal history and body composition goals. Use body fat percentage as your anchor: goal weight = lean body mass ÷ (1 − target body fat %). This gives a target based on actual body composition rather than population averages.

Frequently Asked Questions

What if my goal weight is different from my ideal body weight?

That's completely normal. IBW is a population-average estimate. People with more muscle mass, different frame sizes, or different body composition goals will legitimately have goal weights above or below IBW. Focus on body composition and health metrics rather than an absolute weight number.

How much can weight fluctuate day to day?

Daily weight fluctuations of 2–5 lbs are entirely normal due to water retention, food volume, hormonal changes, and glycogen storage. Weekly averages are more meaningful than daily weigh-ins.