"Locking your rate" sounds like a simple, one-time decision. It isn't quite that simple. A lock guarantees your interest rate for a specific window of time, contingent on your application not changing and your closing happening before the lock expires - and both of those conditions trip people up more often than you'd think. Here's what a lock actually promises, what a float-down really costs, and what happens when a closing runs long.
What a rate lock actually guarantees (and what it doesn't)
A rate lock is your lender's written commitment that your interest rate won't change between now and closing, as long as two conditions hold: you close within the lock period, and nothing material changes on your application. The Consumer Financial Protection Bureau defines it exactly that way - the rate is frozen "as long as you close within the specified time frame and there are no changes to your application."
That second condition is the one people miss. A lock isn't an unconditional promise, it's a promise given the file as submitted. If your credit score drops, your income documentation changes, the loan amount changes, or the property or loan program changes, the lender can reprice the loan even inside an active lock - the lock protects you from market movement, not from changes on your end.
How long does a lock last, and what happens if you run past it
Rate locks are typically offered in 30, 45, or 60-day terms, sometimes longer for new construction or complex files. The lock period needs to comfortably cover the time between your offer and your actual closing date - not just the date on the contract, since closings slip more often than buyers expect.
Here's the part that catches people off guard: the CFPB notes that your Loan Estimate won't tell you what it costs to extend a lock if you need more time. That pricing lives entirely with your individual lender, and it can be expensive. An appraisal delay, a title issue, a slow HOA questionnaire, or a seller who needs an extra two weeks can all push you past your lock date - and if that happens, you're either paying an extension fee, re-locking at whatever rate is current that day, or both.
Standard Rate Lock
Freezes your rate for a set period, typically at no extra cost. If rates fall after you lock, you're stuck with the higher rate unless you paid for a float-down or requalify elsewhere.
Float-Down Option
Lets you drop to a lower rate, once, if rates fall enough during your lock period. Usually requires a nonrefundable fee or a pricing adjustment, and only pays off if the drop clears the lender's threshold.
Rate lock or lock-plus-float-down? Toggle to compare
Both start the same way - you lock a rate before closing. What happens if the market moves afterward is where they diverge.
You lock a rate for 30, 45, or 60 days at no extra charge. If rates rise before closing, you're protected. If rates fall, you're still closing at the rate you locked - there's no built-in mechanism to capture the improvement unless your lender offers one or you shop the loan elsewhere.
You pay an upfront fee, or accept a pricing adjustment, for the right to drop to a lower rate one time if the market falls far enough during your lock window - Chase and other major lenders describe the threshold as typically needing to clear a set minimum, often cited around a quarter of a point. Exercise it once, and you're locked again at the new, lower rate. If rates never drop past that threshold, the fee bought you nothing.
What if you're not sure a float-down is worth paying for? There's a broker-side alternative worth knowing about: because Coltrain isn't tied to a single lender, we can lock your rate with one wholesale lender and, if a genuinely better rate shows up somewhere else before you close, work to switch the loan to capture it - without you having to pay upfront for a float-down that may or may not pay off. It's not guaranteed on every file, but it's an option a single-lender bank simply doesn't have.
What can actually go wrong between locking and closing
Most rate lock problems aren't about the rate itself - they're about timing and paperwork. The lock is only as good as your ability to close inside it.
A slow appraisal, a title search that turns up a lien to clear, a condo or co-op board that takes weeks to approve, or a seller-side delay can all eat into your lock window without you doing anything wrong. Anything that changes your file - a new debt, a job change, an updated loan amount after a low appraisal - can also trigger re-underwriting that outlasts your original lock, even if the calendar days remaining looked fine.
The other common mistake is assuming a float-down is automatic. It isn't. You typically have to request it, confirm you've cleared the lender's rate-drop threshold, and exercise it before closing - miss that window and the option expires along with the rest of the lock.
Should you pay for a float-down?
It depends on how confident you are that rates are heading down, and how much room your closing timeline has. A float-down makes the most sense when your lock is long (45-60 days), rates look genuinely likely to soften, and the fee is small relative to what a real rate improvement would save you over the life of the loan. It makes less sense on a tight 30-day purchase lock where there's little time for the market to move, or when the fee eats most of the potential savings.
Ask about extension cost before you need it. Waiting until the lock has already expired leaves you with no leverage on the fee.
Without a float-down, you're closing at your locked rate regardless - unless your loan hasn't closed yet and switching lenders is genuinely still on the table.
A credit, income, or loan-amount change can let the lender reprice even inside an active lock. Report changes early rather than letting underwriting find them.
Ask what the fee is and what rate-drop threshold triggers it before you pay for one blind. It's a bet, not a guarantee.
Talk to a broker before you lock, not after
The single biggest advantage of working with a broker rather than one direct lender is timing flexibility: we're not committed to one rate sheet. If you're weighing whether to lock now, wait, or pay for a float-down, that's exactly the kind of decision a loan officer should walk through with you against your actual closing timeline - not a generic rule of thumb.
Trying to decide whether to lock now or wait?
What does locking my rate actually guarantee?+
It guarantees your interest rate won't change due to market movement between now and closing, as long as you close within the lock period and nothing material changes on your application - credit, income, loan amount, or property. It does not protect you from repricing if your file itself changes.
How long does a mortgage rate lock last?+
Most locks run 30, 45, or 60 days, occasionally longer for new construction. The lock needs to comfortably cover the real time until closing, not just the contract date, since closings frequently run longer than planned.
What's a float-down, and is it worth paying for?+
A float-down lets you drop to a lower rate, one time, if rates fall enough during your lock period - usually for an upfront fee or a pricing adjustment, and only once a minimum rate-drop threshold is cleared. It's worth considering on longer locks when rates look likely to soften; it's a weaker bet on a short, tight purchase timeline.
What happens if my rate lock expires before I close?+
You'll typically need to extend the lock for a fee or re-lock at whatever rate is available that day, which can be worse than your original rate. Lenders aren't required to disclose extension pricing on your Loan Estimate up front, so it's worth asking directly before you're in a time crunch.
Can I switch lenders after I've already locked a rate?+
With a single direct lender, once you're locked, you're generally locked with them. Working with a broker like Coltrain is different: because we submit loans to multiple wholesale lenders rather than funding from one shelf, if a meaningfully better rate becomes available elsewhere before your loan closes, switching to capture it can still be on the table - something a one-lender bank structurally can't offer.
- Consumer Financial Protection Bureau, "What's a lock-in or a rate lock on a mortgage?"
- Chase, "Float Down Option: Can it Lower Your Mortgage Rate"
