Which score lenders use
Most mortgage decisions use FICO scores from all three credit bureaus, with the middle score used to qualify. For joint applications, lenders typically use the lower of the two borrowers' middle scores.
Typical program floors
FHA can go below 660 in many cases; conventional typically starts at 620 with best pricing above 740; VA has flexible requirements but lenders often layer 580–620 minimums; jumbo programs usually require 700+ with strong reserves. Exact overlays vary by lender.
What helps your score
On-time payments are the largest factor. Keeping revolving balances well below limits, avoiding new tradelines while you're applying, and disputing inaccuracies on your report all support a stronger score.
What hurts during underwriting
Late payments, new collections, new credit inquiries, closing old credit cards (which shortens average account age), or running up balances mid-process can all reduce your score during the loan.