Benzinga and Yahoo Finance LLC may earn commission or revenue on some items through the links below. A house is likely the biggest purchase you will ever make. While homeownership offers many benefits, such as a neighborhood, no roommates above or below you, and a stable place to raise your children, some people buy houses that they can't afford. To avoid that mistake, some people turn to the 30% rule. This rule states that your monthly mortgage payment should not exceed 30% of your gross monthly income. ...