Mortgage rates vary widely within a month, influenced by credit scores, down payments, and lender choice. Improving credit from 680 to 720 can save $3,200 in purchasing power, while a larger down payment above 20% reduces rates modestly but cuts private mortgage insurance costs. Choosing a mortgage broker or correspondent lender can lower rates immediately by about 19 basis points, saving thousands. Shopping lenders and balancing timing with affordability is crucial.