Mortgage lenders pull your credit scores from all three major bureaus: Experian, TransUnion, and Equifax.
For a single borrower: the lender uses the middle score (not the highest or lowest). If your scores are 680, 700, and 720, the lender uses 700.
For two borrowers: the lender takes each borrower's middle score, then uses the lower of those two middle scores. This is why all three scores matter.
How Scores Are Selected
Each bureau may report a different score because they have different data. Lenders pull all three and take the median. This is standard across the industry.
Single Borrower Rules
Single borrower: pull all 3, take the middle score. Example: Experian 710, TransUnion 730, Equifax 700. Middle score: 710. This is the score used for qualification and pricing.
Two Borrower Rules
Two borrowers: Borrower A middle score 720, Borrower B middle score 680. The lender uses 680 (the lower of the two middle scores). Both borrowers' credit matters.
Why Middle Score
The middle score is used because it's the most representative. Using the highest would be too lenient. Using the lowest would be too strict. The median is fair and standard.
Impact of One Low Score
One low score can significantly impact a joint application. If one borrower has a 640 middle score and the other has 780, the lender uses 640. This can mean higher rates or different loan options.
Strategy
If one borrower has significantly lower scores, consider applying separately (if one income is sufficient) or waiting to improve the lower score before applying jointly.