A mortgage rate lock is a written commitment from your lender to hold a specific interest rate, along with any attached points or credits, for a defined number of days while your loan moves through underwriting and to closing. Standard lock periods run 15 to 60 days, and locking shields you from rate increases during that window, though it also means you generally keep the locked rate even if the market improves afterward. Locks are tied to a specific property, loan program, and loan amount, so changes to any of those during processing can reprice your loan, and a lock that expires before you close almost always costs money to extend.
How a Mortgage Rate Lock Works
What the Lock Actually Guarantees
When a loan officer quotes you a rate, that number is not binding. Mortgage rates are priced off mortgage-backed securities that trade throughout the day, and wholesale lenders reissue their rate sheets as the market moves, sometimes more than once in a single afternoon. The quote you got Tuesday morning may not exist Tuesday afternoon.
A lock converts that quote into a commitment. Your lender agrees in writing to honor the rate, points, and lender credits for a set number of days, and assumes the market risk for that period. If rates jump half a point next week, that is the lender's problem, not yours.
What the lock does not do is guarantee your monthly payment. It fixes the interest rate and the associated pricing. Property taxes, homeowners insurance, and mortgage insurance all sit outside the lock and can still shift your final payment.
What Floating Means
Floating means declining to lock and letting your rate move with the market until you decide to commit. Borrowers float when they believe rates are heading down, or when they are too far from closing for a lock to be economical.
Floating is a real strategy, but it is a bet. If rates rise while you float, you absorb the increase, and on a $400,000 loan a quarter point costs roughly $60 a month for as long as you hold the mortgage. Unless you follow bond markets closely and have a specific reason to wait, locking once your file is in underwriting is the more defensible choice.
Lock Periods and What They Cost
Standard Lock Periods
Most wholesale lenders offer locks in 15-, 30-, 45-, and 60-day increments, with longer terms available for new construction and specialty programs. Forty-five days is the workhorse for purchase transactions because it gives underwriting, appraisal, and title enough runway without paying for time you do not need. Thirty days fits refinances and purchases where the file is already complete, and the closing date is firm.
Why Longer Locks Price Higher
Here is the part most articles skip. Lock periods are not free, and the cost is usually buried in the rate rather than shown as a fee.
The longer the lender holds the risk, the more they charge for it, and that charge shows up as a small pricing adjustment baked into your rate or your points. Choosing a 60-day lock when a 30-day lock would have closed the loan means paying for insurance you never used. Ask your loan officer to show you the pricing at each lock period side by side so you can see exactly what the extra time costs before you choose one. Learn more about mortgage discount points.
When to Lock Your Mortgage Rate
Locking on a Purchase
On a purchase, you cannot lock until you have a property address, because the lock is tied to that specific transaction. The practical window opens once your offer is accepted and the contract is executed.
Most buyers should lock at that point, or shortly after the appraisal is ordered. You have a contractual closing date, real money at risk in earnest money, and a hard deadline. That combination leaves very little room to gamble on the market moving in your favor.
Locking on a Refinance
Refinances give you more latitude because neither a seller nor a contract deadline is forcing your hand. If rates are trending down and you have no urgency, floating for a few weeks carries far fewer consequences than it does for a purchase.
The exception is a cash-out refinance to fund something time-sensitive, like paying off a balloon note or funding a renovation with a contractor already scheduled. In those cases, treat the deadline the way you would a purchase contract and lock accordingly.
What Can Break a Rate Lock
Changes That Trigger Repricing
A rate lock is issued against a specific set of loan characteristics: the property address, the loan program, the loan amount, the occupancy type, the credit score used to price the file, and the loan-to-value ratio. Change any of those, and the lender reprices.
This catches borrowers off guard more than anything else in the process. An appraisal that comes in below the contract price increases your loan-to-value ratio and can move you into a higher pricing tier. Switching from conventional to FHA after the lock is issued voids the original pricing entirely. Even reducing your down payment to keep cash in reserve can push your loan-to-value across a threshold and cost you a fraction of a point. For more on loan types, see FHA vs Conventional Loan: A Comprehensive Comparison.
Costs a Rate Lock Does Not Cover
Your locked rate governs interest-rate-dependent charges. It does not freeze third-party costs. Title fees, recording fees, appraisal fees, and escrow deposits for taxes and insurance can all vary between your initial estimate and your final numbers, within the tolerance limits allowed by the disclosure rules.
The Loan Estimate Rule That Follows Your Lock
Why Your Lock Date Matters
Federal disclosure rules build a specific protection around the moment you lock, and almost no borrower is told about it. Once your rate is locked, your lender must send you a revised Loan Estimate within 3 business days, showing the locked rate, points, lender credits, and any other charges that depend on the rate. That revised disclosure is required even when nothing about your terms actually changed.
This matters because it is a requirement, not a courtesy. If you lock and no updated Loan Estimate arrives within three business days, something is wrong with how your file is being handled, and that is worth asking your loan officer directly.
The Closing Disclosure Cutoff
There is a hard stop on the back end. Once your lender issues the Closing Disclosure, they are no longer permitted to send a revised Loan Estimate, and that holds even if you lock your rate after the disclosure goes out.
The practical consequence is that locking very late in the process removes your lender's ability to reset the pricing baseline through a revised estimate. It is one more reason to lock while your loan is still in underwriting rather than in the final days before closing.
Extensions, Relocks, and Float Down Options
What an Extension Costs
Locks expire, and closings slip. When a lock is about to expire before you can close, the lender will offer an extension priced as a fraction of a point on your loan amount, typically charged per block of additional days and paid at closing.
Extensions are usually the cheaper outcome. Letting a lock expire outright often triggers worst-case pricing, meaning the lender reprices your loan at the higher of the original locked rate or the current market rate. If the market moved against you while your file sat, you pay the new rate.
How Float Downs Work
A float-down is an option attached to a lock that lets you capture a rate improvement if the market drops far enough before you close. It is not automatic and not universal. Float downs carry a cost, require the market to move by a defined threshold before you can exercise them, and come with a window for using them.
They are worth asking about specifically, because a float down is only valuable if rates fall by more than the option costs you. When rates are flat or rising, that fee buys nothing.
Locking Through a Broker Instead of a Single Lender
A bank can only lock you into its own rate sheet. A brokerage compares pricing across multiple wholesale lenders before the lock is placed, which means the comparison happens at the one moment it actually changes your outcome.
That difference shows up in the lock periods too. Different wholesale lenders price 45- and 60-day locks differently, and a file with a longer runway may cost meaningfully less at one lender than another for the same rate. At Flagstone Mortgage, we shop your file across our lender panel before locking and show you the pricing at each period so the decision is yours to make with real numbers in front of you.
If you are under contract or considering a refinance, get a quote or contact our team, and we will walk you through your lock strategy before your timeline forces a decision.