Yes, they vary widely. If you control for certain variables, they can give you decent directional information.
One of the biggest factors in the accuracy of the older Tanita brand scales (this is the brand I have had for many years) is your hydration. For example, if you weigh right when you get out of the shower (even toweled dry), your reported body fat will be much lower than your reported body fat before the shower.
They are also sensitive to callouses on your feet.
My brother reports much more consistent results with a handheld body fat analyzer, but I've never tried one on a consistent basis.
One of the biggest factors in the accuracy of the older Tanita brand scales (this is the brand I have had for many years) is your hydration. For example, if you weigh right when you get out of the shower (even toweled dry), your reported body fat will be much lower than your reported body fat before the shower.
They are also sensitive to callouses on your feet.
My brother reports much more consistent results with a handheld body fat analyzer, but I've never tried one on a consistent basis.