Mortgage Rate Lock Explained

A rate lock is a lender's promise to hold your rate and points for a set number of days while your loan is processed. Locking too early or too late both carry risks — here is how the decision works.

What a rate lock actually is

When a lender quotes you a rate, that number is only a snapshot of that day's market. A rate lock converts the snapshot into a commitment: the lender guarantees that rate and set of points for a specific window, typically 15 to 60 days, while your application moves through underwriting to closing. If market rates rise during the window, you keep your locked rate. If rates fall, you generally keep your locked rate too — the protection runs both ways, which is the trade at the heart of every lock decision.

Lock periods and why length matters

• 15–30 days: cheapest pricing, but only realistic if your loan is nearly ready to close.
• 45 days: the common middle ground for a standard purchase.
• 60 days: costs a little more, but suits new construction or slow transactions.

Longer locks cost more because the lender carries the market risk for longer. The price difference between lock lengths is usually small — often an eighth of a point or less in rate terms — but on a $400,000 loan, where principal and interest at an illustrative 6.5% is $2,528 a month, even small rate differences add up over the years.

What if your lock expires?

If closing slips past the lock window, you will usually pay an extension fee. Extensions are commonly priced per day or as a small fraction of the loan amount, and repeated extensions get expensive. Worse, if the lock lapses entirely and rates have risen, the lender may reprice the loan at the worse of the locked rate or the current market. The practical defense is boring but effective: choose a lock length that matches your realistic closing timeline, and respond to document requests quickly so underwriting does not stall.

Float-downs: the middle option

Some lenders offer a float-down: you lock, but if rates improve by a set amount before closing, you can take the lower rate once. Float-downs may be free or carry a fee, and the trigger is usually a meaningful improvement, not a tiny daily wiggle. Ask about the float-down policy before you lock, not after rates move — it is a term of the lock agreement, and it cannot usually be added later.

When should you lock?

There is no formula, but experienced loan officers tend to work from these principles:

1. Lock when the payment fits your budget comfortably. On a $300,000 loan, an illustrative 6.5% gives $1,896 a month in principal and interest; if that number works for you, protecting it has real value. Test your comfort level with the payment calculator.
2. Lock sooner when your closing is near. The shorter the remaining timeline, the less time rates have to fall in your favor anyway.
3. Floating is a gamble with your housing payment. If a rate rise would break your budget or your debt-to-income approval, the gamble is not worth taking. Understand your approval limits via the DTI guide.
4. Never lock before you have a signed purchase contract on a specific property in most purchase situations — locks attach to real transactions with deadlines.

Before you lock, confirm these details

Get the lock in writing, and check the rate, points, lock period, expiration date and float-down terms. Confirm whether the quote includes lender fees that could change, and ask what happens if the appraisal delays closing. A lock protects the rate; it does not protect you from an unrealistic timeline. Borrowers comparing two lenders should also confirm each lock's length, since a cheaper 15-day lock and a standard 45-day lock are not the same product — the comparison calculator helps line the offers up honestly.

A rate lock is insurance against market movement during the most stressful month of the homebuying process. Priced right and matched to your timeline, it turns an unknown into a fixed number you can plan around — which, for most buyers, is worth more than squeezing out a hypothetical extra eighth of a point.

Run your own numbers

Before you lock, read the mortgage rates guide, compare your competing offers in the comparison calculator, and verify the payment math with the step-by-step payment guide.