What is a mortgage rate lock?
Short answer
A rate lock means the offered interest rate will not change through closing if you close on time and your application does not change. Common lock windows are about one to two months, and some lenders offer longer periods. A lock can still change if loan amount, credit, income, or other application details change.
Full explanation
A lock-in holds the quoted interest rate from the offer through closing when you finish on time and the application stays the same. Quoted rates can move from one day to the next. Without a lock, the rate can move until you close.
Typical lock windows run about one to two months, and some lenders offer longer ones. Buying more time later can be costly. A lock can also mean you do not get a later drop in market rates. Some lenders lock when they issue a Loan Estimate; others wait. Page 1 of the Loan Estimate shows whether a lock is in place and how long it lasts.
A lock is not unconditional. Changing the product, the amount borrowed, or the down payment can reopen the rate, as can an appraisal that differs from expectations, a new account or missed payment that moves your credit, or overtime or bonus income the lender cannot verify. Ask the lender what the lock covers, what it costs to extend, and what happens if closing is delayed or rates fall.