Screw BMI
Body Mass Index (BMI) charts are wrong and useless and should be ignored. They're only used because they're easy: plug in height and weight, compare to The Chart Of Truth, and you're done. But they aren't useful for individuals to predict the bad health outcomes we want to avoid. BMI causes so many false "healthy" and false "unhealthy" results that it's simply not trustworthy.
BMI was designed to be used for populations. If you're basing your workout, diet, or health goals on BMI, you've done something wrong. It's only a mistake of history that we still use BMI. It should be discarded.
Screw IBW
"Ideal Body Weight" calculations come with a disclaimer:
The IBW and ABW are used to calculate medication dosages when the patient is obese.
Alternatively:
Ideal Body Weight, specifically the Devine Formula, is used clinically for multiple reasons, most commonly in estimating renal function in drug dosing, and predicting pharmacokinetics in morbidly obese patients.
So-called "ideal" body weight calculations are not in any way supposed to be used as a guideline for how much weight to lose. Do not allow them any power over your life.
Superior Alternatives
Using BMI or IBW to measure how much you should weigh is pointing your efforts at the wrong goal. If you want to be lean, work on your body fat percentage. If you want to be healthy, work on strength, conditioning, and mobility goals. (If you're tremendously overweight, picking a goal weight for your initial weight loss can work, but there's absolutely no reason to bring BMI into it, and once that goal weight is reached, it's better to target more useful numbers.)
Instead of targeting a specific BMI goal, measure what you want to improve. Want to look better? Get a camera and a tape measure and track how you look (with consistent clothing, pose and lighting) and measurements of your arms, legs, hips, and waist. Or set a performance goal, like "finish a 5k" or "squat twenty times with a barbell as heavy as I am". Want to be healthy? Develop a strength and conditioning program to work towards your desired health markers, like body fat percentage.
The closest useful analogue to BMI is the Body Shape Index, which seems to be a better predictor of one's risk of death. Keep in mind that while it takes belly fat into account, it still does not keep track of muscle or actual markers of physical health, like mobility, strength, inflammation, diabetic state, or cardiovascular disease.
Body Shape Index= Waist Circumference/[(BMI^(2/3))*(height^(1/2))]
