Mortgage Rate Locks Explained: When to Lock and What a Float-Down Actually Does

At some point in a purchase or refinance, a loan specialist will ask a version of the same question: do you want to lock your rate now, or wait? It sounds like a coin flip on where rates go next. It isn't. A rate lock is a timing and risk decision tied to your closing date, not a bet on the bond market — and the float-down option that sometimes comes with it is more limited than most borrowers expect.

Here is what a lock actually does, how long it typically holds, what happens if it runs out before you close, and where a float-down does and doesn't help.

What a rate lock actually does

A rate lock is a lender's commitment to hold a specific interest rate and pricing for your loan for a set period of time, regardless of what happens in the broader market between now and closing. Once locked, day-to-day rate movement — up or down — generally doesn't change your quoted rate, as long as your loan closes inside the lock window and your loan terms don't change.

That last part matters. A lock is tied to a specific loan amount, loan-to-value ratio, credit profile, property type, and program. If any of those shift materially between locking and closing — a lower appraisal, a credit score change, a different loan amount — the lender can reprice the loan even with an active lock. The lock protects you from market movement, not from changes to your own file.

For current pricing, check the rates page rather than relying on a number from a past conversation or a competitor's ad — pricing changes daily and varies by borrower and program.

How long a lock typically lasts

Lock periods commonly range from roughly 15 to 60 days, with 30 and 45 days being the most typical choices for a standard purchase or refinance. Some lenders offer longer locks — sometimes 90 days or more — for new construction or other transactions where closing is expected to take longer.

The right length is less about preference and more about matching your realistic closing timeline: appraisal scheduling, underwriting, and any conditions still outstanding on the file. Locking for a period shorter than your likely closing date is a common way borrowers end up paying for an extension they didn't plan for. Locking far longer than needed is not free either — pricing for longer lock periods is often less favorable than for shorter ones, so there's typically a tradeoff between certainty and cost that's worth discussing with the loan specialist rather than assuming the longest lock is automatically the safest choice.

What happens if the lock expires before you close

If a loan doesn't close inside its lock window, the file generally falls into one of a few outcomes, depending on the lender and the reason for the delay:

• A paid or fee-based extension. Many lenders will extend a lock for an additional period in exchange for a fee, sometimes reduced or waived if the delay was the lender's fault (for example, a slow underwriting turnaround).
• Relocking at current market pricing. If an extension isn't offered or requested in time, the loan may need to relock at whatever pricing is available on the new date — which could be better or worse than the original lock.
• A short automatic grace period. Some lenders build in a small buffer before a lock is treated as expired, but this varies and shouldn't be assumed without confirming it for your specific loan.

None of these outcomes are catastrophic, but all are easier to manage if you're tracking your lock expiration date against your closing timeline from the start.

What a float-down option actually is

A float-down is an add-on to a rate lock that lets a borrower capture a lower rate if market rates drop meaningfully after locking, without giving up the protection of the original lock if rates instead rise. It is not automatic, and it is not free in most cases — many lenders either charge an upfront fee for the option or build its cost into the locked rate itself.

A few things a float-down generally is not:

• It is not unlimited. Most float-down options allow one adjustment, not ongoing repricing every time the market moves.
• It does not trigger automatically. Borrowers typically have to request the float-down and often must do so within a defined window before closing, not at any point during the lock.
• It usually requires a minimum rate improvement. Many programs only allow a float-down if rates have dropped by more than a small threshold — a modest dip that doesn't clear that bar generally won't qualify.

Whether a float-down is worth paying for depends on your read of near-term rate direction, how far out your closing is, and what the option costs relative to the potential savings. That's a program-specific comparison the loan specialist can run against your actual numbers rather than a general rule that applies the same way to every file.

When locking early makes sense — and when waiting might

Locking as soon as you're comfortably under contract or far enough into a refinance removes the guesswork: your payment math is set, and you can plan around it. That tends to make sense when your timeline is tight or the current pricing already works for your budget.

Waiting can make sense if your closing date is genuinely far out and locking early would mean paying for a longer lock period than you need yet. It rarely makes sense to wait purely because you're hoping to "beat the market" — that's a prediction, not a strategy, and the downside if rates move against you is real.

Purchase vs. refinance: does the calculus change?

The mechanics of a lock and a float-down work the same way whether you're buying or refinancing, but the timing pressure differs. A purchase lock is anchored to a contract closing date that usually isn't very flexible — sellers and other parties are on the same clock. A refinance generally gives you more control over when you start the clock, since there's no counterparty pushing for a closing date, which can make it easier to time a lock around your own read of the market or around a specific rate target.

That flexibility is also why refinance timing gets evaluated against a different question entirely: whether the numbers justify refinancing at all, independent of when you lock. If you haven't run that math yet, refinance break-even math walks through the formula that answers it.

Questions to ask the loan specialist

• What lock period matches my realistic closing timeline, with some buffer?
• What does an extension cost if the loan doesn't close in time, and does that cost depend on why it was delayed?
• Does this program offer a float-down, what does it cost, and what minimum rate movement triggers it?
• Is there a window during which I have to request the float-down, and when does it close?
• If my loan amount, LTV, or credit profile changes before closing, does my locked rate still apply?

Common mistakes

• Locking for a period shorter than the realistic closing timeline. A tight lock window turns routine underwriting delays into extension fees.
• Assuming a float-down is automatic. Most require an active request within a specific window, not a passive right that applies whenever rates drop.
• Waiting to lock purely to "beat the market." That's a prediction, not a strategy — and it cuts both ways.
• Not confirming what happens if loan terms change. A different appraisal value, credit score, or loan amount can affect pricing even under an active lock.

The bottom line

A rate lock is a timing tool, not a market call — it protects your pricing for a defined window that should match your realistic closing date, with some buffer. A float-down can add flexibility if rates drop, but it typically has to be requested, often has a minimum threshold to trigger, and usually isn't free. The details — lock length, extension costs, float-down terms and pricing — vary by lender and program, so confirm them against your specific file rather than assuming they match what a friend's lender offered on a different loan.

Start a purchase scenario or contact a BetterOffers loan specialist to talk through lock timing against your actual closing date. Related reading: Mortgage Rates Rising: Should You Lock Now? for a market-timing perspective, and Why HELOC Rates and Cash-Out Refinance Rates Are Different if you're weighing a rate-sensitive decision beyond a first mortgage. Financing remains subject to application, documentation, credit, property review, current product availability, and final underwriting.

This article is for general education only and is not financial, legal, or lending advice. It is not a commitment to lend or an offer of credit. Rate lock periods, extension policies, float-down availability, costs, thresholds, rates, APRs, payments, and underwriting requirements vary by lender, program, borrower, property, transaction, and market conditions.