It's an informational estimate, not a pre-qualification. The math models the four levers underwriters actually use (DTI, credit, cash to close, reserves) with weights that match how Fannie Mae, Freddie Mac, FHA, and VA prioritize them, so it tends to be a reasonable directional read for the average buyer in California.
Where it's less precise: it doesn't know about niche programs you might fit (VA, USDA), recent credit events, gift funds, or non-W2 income. That's what the call after the coach is for, to take the estimate and tune it to your actual situation.