Is balding really inherited from the mother's side?

Partly. The "look at your mother's father" rule of thumb is a real thing but only captures part of the story.

The biggest single genetic contributor to male-pattern baldness is a variant in the androgen receptor gene (AR), which sits on the X chromosome. Men have one X chromosome, inherited from their mother. So a man's androgen receptor variant comes from his mother, and his mother's X chromosomes came from her father (one of them) and her mother (one of them). This is the basis of the old wives' tale.

But baldness is genuinely polygenic. A 2017 study identified more than 200 genetic markers associated with male-pattern baldness, located across many chromosomes - not just the X. Variants on chromosome 20 (near the PAX1/FOXA2 region) have particularly large effects. These can come from either parent.

So the practical picture: looking at your maternal grandfather is informative, but not definitive. A man whose maternal grandfather was bald has somewhat elevated risk. A man whose paternal grandfather and father are both bald also has elevated risk. The two add up.

The "blame your mother" version of the story was based on real biology but oversold the X-chromosome contribution. The full picture is more democratic - and harder to escape.