How to Read a Mortgage Rate Lock (And When to Use One)

A mortgage rate lock is a lender's written commitment to hold a specific interest rate for a defined period — typically 30, 45, or 60 days — while your loan application is processed and your closing is scheduled. Without a lock, your rate floats with market conditions, which can work in your favor or against you.

Rate locks became a particularly high-stakes decision in 2022–2023, when rates moved more than 3 percentage points in under 12 months. Buyers who floated and hoped for improvement often watched their monthly payment increase by hundreds of dollars between contract and close. That experience has made rate locks a standard practice even for buyers who might otherwise be comfortable with short-term uncertainty.

The mechanics of a rate lock are straightforward: your lender quotes you a rate, you sign a lock agreement, and that rate is held until the specified expiration date. Most locks at 30 days are free; longer locks typically cost the borrower either a small upfront fee (0.25–0.5% of the loan amount) or a slightly higher rate to compensate the lender for holding the risk.