Quick correction before we go further: pre-approval does not lock your rate. That's a common enough mix-up that it's worth stating plainly, because the number your loan officer quotes you during pre-approval is a floating estimate, not a promise. It moves with the market every single day until you actually lock it — which, in most cases, doesn't happen until you're under contract on a specific house.

So what actually is a rate lock?

A rate lock is a lender's written guarantee that your interest rate won't change between now and closing, as long as you close within the agreed window and nothing material changes about your loan (credit score tanking, income you can no longer document, an appraisal that blows up the loan amount, etc.). It freezes the number. Rates could spike the week before your closing and it wouldn't touch you — that's the entire point of paying for the privilege, when you do pay for it. The Consumer Financial Protection Bureau frames it the same way: a lock protects you from rate movement between the offer and closing, provided you close on time.

When can you actually lock — and why not at pre-approval?

Your first real shot at locking a rate is typically after you've signed a purchase agreement and your lender has issued a Loan Estimate for that specific property, per The Mortgage Reports. Makes sense when you think about it: a lock is tied to a specific loan amount, on a specific property, with a specific lender. At pre-approval, you don't have any of those things nailed down yet — you're shopping, not committing. Some lenders will let you lock earlier if you're deep into underwriting with a firm closing date, but "lock at pre-approval" isn't really a thing most lenders offer, and treat any lender who implies otherwise with a raised eyebrow.

How long does a lock last, and what does it cost?

Standard lock periods run 30, 45, or 60 days, with longer options — sometimes 90 or 120 days — available for a fee, per Bankrate and Consumer Financial Protection Bureau. New construction, which can drag on for months, is the classic case where you'll see the longer windows offered upfront.

A lock inside the standard window (30–45 days) is usually free or baked into your rate — lenders price it in rather than itemizing it. Go longer than that and you'll typically pay for it, either as a flat fee or a percentage of the loan, in the range of 0.25% to 1% of your loan amount, per Bankrate. On a $400,000 loan, that's roughly $1,000 to $4,000 just to buy more time upfront — which is exactly why "lock long to be safe" isn't automatically the smart move.

Float-down options: paying to keep your options open

A float-down lets you claim a lower rate if the market drops after you've locked, instead of being stuck with your original number. Two things to know about it: it's usually an add-on you have to request and pay for, not something that happens automatically just because you locked, and most lenders require rates to drop by a minimum threshold — commonly around 0.25% to 0.5% — before you're eligible to exercise it, according to Rocket Mortgage.

The fee structure mirrors extension fees: often 0.25% to 1% of the loan amount, non-refundable whether or not rates actually drop enough to use it. On that same $400,000 loan, you could be paying $1,000–$4,000 for a maybe. Chase is blunt about the tradeoff: the fee can outweigh the benefit depending on how rates actually move, and not every lender offers it in the first place — ask early if it's something you want, not the week before closing.

What happens if closing gets delayed past your lock?

This is the scenario that should actually shape your timing decision. Financing falls through, appraisal comes in low and everyone needs a week to renegotiate, seller's attorney disappears for a long weekend — closings slip constantly, and your rate lock does not care about your excuses. Two things can happen:

  1. You pay an extension fee to push the lock out further. Costs vary widely by lender — Bankrate cites examples like a flat $595 for a 60–90 day extension at one lender and $1,500 for a 120-day lock at another, alongside percentage-based fees in the same 0.25%–1% range as float-downs.
  2. You relock at current rates if your lender won't extend or you let it lapse, which means eating whatever the market is doing that week — could be nothing, could be a full point higher. Given the Freddie Mac weekly average has bounced around notably even in the past year (6.67% as of August 13, 2026, versus 6.58% a year earlier), "wait and see" is a real gamble, not a neutral choice.

Some lenders waive the fee if the delay is on them rather than you — worth asking about explicitly before you sign a lock agreement, per CBS News.

So when should you actually lock?

The honest answer is: once you have a signed purchase agreement and a closing timeline you're reasonably confident in — not the moment you find a house you like, and not the day before closing either.

  • Lock too early, before your closing date is solid, and you risk needing a costly extension if anything slips (and something almost always slips a little).
  • Float too long, waiting for a "perfect" moment, and you risk the market moving against you before you commit — with no guarantee it moves your way instead.

A reasonable rule of thumb: once your offer is accepted, your loan is in underwriting, and your lender gives you a realistic closing date, lock into a window that comfortably covers that date with some cushion — not the bare minimum. If your closing timeline looks tight or unusual (new construction, a complicated chain, a short-sale situation), that's when the longer, paid lock windows or a float-down actually start to earn their fee instead of just being an insurance policy you didn't need.

This is also a good moment to actually talk to your loan officer instead of guessing: ask what their standard lock window costs, what an extension costs if you go over, and whether float-down is even offered. Those numbers vary enough by lender that a generic answer isn't going to be precise enough to act on — get the real figures for your deal before you sign anything.

Sources

Fee figures above (extension costs, float-down costs) are drawn from lender examples cited in the sources listed and vary by lender —.