Mortgage Rate Locks Explained: When to Lock, Float, and What Extensions Cost

A rate lock guarantees your interest rate for a set period while your loan moves through underwriting. It sounds simple, but the timing decision — and what happens when your closing date slips — trips up a lot of buyers who don't understand the mechanics until they're mid-transaction.

What a lock actually does

Once you lock, your rate is fixed for the lock period regardless of what happens in the broader rate market — if rates rise after you lock, you're protected; if rates fall, you're generally stuck at your locked rate unless your lender offers a float-down (more below). The lock applies to your interest rate and, if you're paying points, the associated pricing — it does not lock your loan amount, which can still shift if your appraisal comes in differently than expected or your final numbers change.

Typical lock periods and what they cost

Common lock windows are 15, 30, 45, and 60 days, with some lenders offering longer locks (90+ days) for new construction or extended timelines. As a general rule, longer locks cost more — either as a flat fee, a higher rate (a few hundredths of a percentage point per additional 15-day increment is typical), or both. A 30-day lock is often free or built into standard pricing; a 60-day lock might cost an extra 0.125%-0.25% in rate or an upfront fee, varying by lender and loan program.

Match your lock period to your realistic closing timeline, not the optimistic one. If your purchase contract has a 45-day close and there's any chance of appraisal delays, title issues, or a slow seller, consider locking for 60 days rather than 45 — the cost of a longer lock is almost always less than the cost of a rate-lock extension fee if you run out the clock.

What happens if your closing date slips past your lock expiration

You'll need an extension, and extensions are priced less favorably than locking longer from the start — commonly 0.125%-0.375% of the loan amount per week, or an equivalent rate increase, depending on the lender and how far past expiration you are. If the delay is the lender's fault (they were slow processing your file), some lenders will absorb the extension cost; if it's due to seller delays, title issues, or appraisal disputes, you're typically on the hook. Ask your loan officer directly, in writing, who pays for likely extensions before you're in the situation — it's a much easier conversation before there's a deadline pressure.

Float-down options

Some lenders offer a float-down provision — usually for an upfront fee (flat dollar amount or a fraction of a point) — that lets you capture a lower rate once, if rates drop meaningfully after you lock but before you close. Terms vary: some require a minimum rate improvement (say, 0.25%) to trigger it, some allow only a single float-down request, and some only apply within a specific window before closing. If you're locking early with a longer timeline and rates are volatile, ask specifically whether float-down is available and what it costs — it can be worth it as insurance against locking too early in a falling-rate environment.

Lock vs. float: a decision framework

• Lock immediately if: you have a firm closing date under 45 days, rates have been trending up, or you simply want payment certainty for budgeting and can't tolerate the anxiety of a floating rate during underwriting.
• Consider floating a bit longer if: your closing is 60+ days out, there's a scheduled economic event (Fed meeting, major data release) that could move rates favorably, and your lender offers a reasonable float-down option as a backstop.
• Always lock before: submitting final loan approval documents or scheduling your closing date — closing without a locked rate exposes you to whatever the market rate is on your actual closing day, which is not a position you want to be negotiating from at the closing table.

What a rate lock does NOT protect you from

Your rate is locked, but your total payment can still move if: property taxes or insurance estimates change, the appraisal comes in different than expected (changing your loan-to-value and possibly your mortgage insurance rate), or you make changes to your loan structure (switching loan type, changing down payment amount) after locking, which typically requires a new lock. A rate lock is not a purchase price lock, a payment lock, or a guarantee your loan closes — it only fixes the interest rate on the specific loan terms you locked.

Get it in writing

Always request a written lock confirmation showing the exact rate, the lock period start and expiration dates, any points paid or credited, and the specific loan terms (loan amount, program, term) the lock applies to. Verbal confirmations from a loan officer are not enforceable the way a written lock confirmation is — if there's ever a discrepancy at closing, the written confirmation is what protects you.

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