Home loans above $625,500 in high-cost areas will be considered "jumbo" mortgages after Sept. 30, and will carry a higher interest rate than so-called conforming loans below that threshold. Right now, the jumbo loan cutoff in many high-cost areas, including most Bay Area counties, is $729,750.

The change means Buyers who need a loan between $625,500 and $729,950 will now pay 0.50 to 0.75% more for their financing than they would have before the change. What's more, because of the higher borrowing cost, their maximum purchase price will be reduced accordingly. As an example, using today's rates, a Buyer with 20% down who was qualified to purchase an $850,000 home prior to the change would only qualify for a $790,000 home after the change because of the higher monthly payment under the new rules.