Rate Lock Explained: When to Lock and What It Costs to Extend

A rate lock is an agreement with a lender to hold a specific interest rate for a set period of time while a loan moves through processing and underwriting toward closing. Without a lock, the quoted rate can change before closing, since mortgage rates move daily based on market conditions.

Why locking matters

Rates can move between application and closing, sometimes significantly over a few weeks. Locking removes that uncertainty for the length of the lock period, giving a buyer a fixed number to plan around rather than a moving target.

Typical lock periods

Lock periods commonly range from around 15 to 60 days, though longer locks are sometimes available, usually at a higher cost. The right length generally depends on how long the closing timeline is expected to take — a purchase with a fast closing date needs a shorter lock than new construction with a longer, less predictable timeline.

What locking typically costs

Shorter lock periods are often included at no additional cost as part of standard loan pricing. Longer lock periods, or lock extensions, typically come with an added cost, either as an upfront fee or a slightly higher rate, since the lender is taking on more rate-movement risk over a longer window.

What happens if closing takes longer than the lock

If a closing is delayed past the lock expiration for reasons outside the borrower's control, lenders often allow an extension, usually for an additional fee. If a lock expires without an extension, the loan may need to be re-locked at current market rates, which could be higher (or occasionally lower) than the original locked rate.

Float-down options

Some lenders offer a "float-down" option, allowing a borrower to take advantage of a rate decrease during the lock period, typically for an additional fee or as a feature of certain loan programs. Without this feature, a standard rate lock generally only protects against increases — it doesn't automatically pass along a decrease.

When to actually lock

There's no universally "right" time — locking early provides certainty but forgoes any chance of a rate drop before closing; waiting keeps flexibility but carries the risk rates rise in the meantime. Many buyers lock once a purchase contract is signed and a realistic closing date is known, since that's when the lock period can be matched more precisely to the actual timeline.

Where to review lock terms carefully

Lock agreements should specify the exact rate, the lock period length, and any conditions for extensions — details worth reviewing directly with the lender rather than assuming standard terms apply. The Consumer Financial Protection Bureau's rate lock overview explains typical lock terms and questions to ask a lender.

Compare locked-in numbers before committing

Once a rate is locked, it's worth confirming the resulting payment matches expectations. Use MortgageWise.online's free calculator to check your locked rate against your target monthly payment before finalizing the lock.