When you lock a rate, your lender is guaranteeing you that rate for a specific amount of time, whether rates go up or down, you get the rate agreed upon at the time of locking. However, market rates can change daily, and rates could go down while your house is being built.

Mortgage rates will fluctuate up and down based on the market. Rates can change daily, so you don't know what your rate will be until you lock it. By locking a rate, your lender is guaranteeing you that rate for a specific amount of time, typically 30-45 days. Once you lock your rate, it doesn’t matter if the market fluctuates. If you locked at 4 percent and rates go up, you still get the 4 percent. The risk is on the lender when you lock a rate.  However, if rates go lower, you don’t get the benefits of a lower rate.