How Do Mortgage Rate Locks Work?
A mortgage rate lock is a lender's written commitment to hold your interest rate steady for a defined period — from the day you lock through the day you close. If rates climb while your loan is in underwriting, you're protected. If rates drop, you stay at the locked rate unless you have a specific add-on to handle that. Here's how the whole thing works.
What Is a Rate Lock, Exactly?
Mortgage rates move daily — sometimes multiple times a day — driven by bond markets, economic reports, and Federal Reserve policy. When you're under contract to buy a home, that movement is a risk you don't want hanging over your transaction.
A rate lock eliminates that variable. Once locked, your lender commits in writing to honor that rate as long as your loan closes within the agreed window. That locked rate is the one that shows up on your Loan Estimate and Closing Disclosure — no surprises at the table.
When Should You Lock Your Rate?
Timing a lock comes down to where you are in the process. Most borrowers lock at one of three points:
- At contract — the most common moment; you've identified a property, signed a purchase agreement, and have a realistic close date in sight
- At pre-approval — rarely available this early, since lenders need a specific property and loan amount
- During underwriting — if you chose to float through early processing, lock before the file goes to an underwriter
For buyers in the Antelope Valley and Los Angeles County, a standard purchase runs roughly 30–45 days from contract to close. That timeline drives the lock conversation. If your transaction involves contingencies that could push the close date, understanding how contingencies work is worth doing before you commit to a lock window.
If you haven't gone through mortgage pre-approval yet, that step comes before any lock discussion — you can't price a lock without a loan amount and a target close date.
How Long Does a Rate Lock Last?
Lock periods typically run 15, 30, 45, or 60 days. Thirty- and 45-day windows cover most standard purchases. New construction and complex transactions sometimes need 90-day locks or longer.
The rule: lock for the time you actually need, plus a reasonable buffer. A 30-day lock on a deal that realistically needs 35 days creates pressure nobody wants. A few extra days of protection is almost always worth the minor cost difference.
Lock length and pricing are connected. Shorter windows tend to cost less because the lender's exposure is limited. Longer windows cost more — either through a slightly higher rate or an upfront fee — to compensate for holding that commitment while the market moves.
What Does a Rate Lock Cost?
The pattern across most lenders:
- Short locks (15–30 days): Cost is often embedded in the base rate, with no separate line item
- Mid-range locks (45–60 days): May carry a small premium — either a fee or a marginally higher rate
- Extended locks (90+ days): Usually priced explicitly; some require a non-refundable deposit
Before you lock, confirm exactly what you're paying and when. California mortgage closing costs already have plenty of line items — knowing where the lock fee sits, and whether it's refundable if the deal falls apart, is part of doing this right.
What Happens If My Rate Lock Expires?
Missing your lock window is expensive. If your loan doesn't close before expiration, you have two options:
- Extend the lock — available from most lenders, but not free; extension fees are typically calculated per day or per week as a percentage of the loan amount
- Re-lock at market — if rates have moved against you since you originally locked, this is the painful scenario
The most common causes of expiration: appraisal delays, title issues, slow underwriting conditions, and seller-side problems outside your control. The best defense is moving fast on every condition your lender sends after you go under contract. If you're curious what an aggressive timeline actually looks like, fast lending in California breaks down what drives — and delays — closings.
Can I Get a Lower Rate After Locking?
Standard rate locks are one-directional: you're shielded from rate increases, but you don't automatically benefit if rates fall. That changes if you add a float-down option.
A float-down lets you capture a lower rate if the market drops by a defined threshold before closing. It costs extra upfront, and the mechanics vary — how much rates need to move, when you can exercise the option, and what portion of the rate is eligible. Not every lender offers them, and not every market environment makes them worth the cost.
The calculation: weigh the float-down fee against your realistic expectation that rates will fall far enough to offset it before you close. If you're within a week or two of closing, the math rarely works in your favor.
What's the Difference Between Locking and Floating?
"Floating" means you've deliberately not locked — your rate follows the market until you decide to commit. Some borrowers float when they expect rates to fall and want to time the dip. The risk: rates can move against you quickly and without warning.
For most borrowers, floating only makes sense when there's a clear near-term catalyst for rates to drop and you have time to wait. If your qualification depends on a specific payment range, floating is speculation you don't want. Understanding how mortgage rates are set gives you a clearer picture of what you're betting on.
Rate Locks on Refinances
Everything above applies to refinances, with one difference: you have more control over the timeline. There's no seller, no competing contingency, no third-party contract deadline. That's an advantage — but it also means the scheduling risk falls on you.
If you're weighing a refi and watching rates, the best time to refinance isn't just about where rates sit today — it's about whether your loan can actually close fast enough to capture the rate you're targeting. Rates can reverse in days.
Questions to Ask Before You Lock
Don't lock without getting straight answers to these four:
- What lock period makes sense for my transaction timeline, and why?
- What does extending cost if we need more time?
- Do you offer a float-down option, and what's the trigger threshold?
- Is any upfront lock fee refundable if the deal falls apart?
A confident loan officer answers all four without hedging. Vague responses are a signal to keep shopping.
At Fast Financial (NMLS #2226871), the lock conversation is part of every rate review — not an afterthought. See where you stand and we'll walk through the right window for your transaction.
Frequently asked questions
What is a mortgage rate lock?
A mortgage rate lock is a written commitment from your lender to honor a specific interest rate for a set period while your loan closes. Once locked, market rate changes don't affect the rate on your loan — as long as you close before the window expires.
Can I lose my rate lock?
Yes. If your loan doesn't close before the expiration date, you'll need to pay to extend or re-lock at current market rates — which may be higher. Moving quickly on lender conditions after going under contract is the most reliable way to protect it.
Does locking a rate trigger a new credit pull?
No. Locking your rate does not generate a new credit inquiry or affect your credit score. The credit pull happened earlier, during your pre-approval or application.
What happens if rates drop significantly after I lock?
A standard lock doesn't adjust downward on its own. Ask your loan officer whether a float-down option is available — it allows you to capture a lower rate if the market moves by a defined amount before closing, though it typically carries an added cost.
Can I switch lenders after locking?
You can, but you'd forfeit your existing lock. Any new lender would price a new lock at current market rates on the day you apply with them. Factor in both the rate difference and any time lost before switching.