Your rate lock has an expiration date, and closing delays don't care
A rate lock is not indefinite protection. It expires on a set date, and if your closing slips past that date for any reason, you do not automatically keep the rate you locked. You pay to keep it, or you take whatever rate the market is offering that day. Most lenders explain the lock. Fewer explain what happens when it runs out.
A composite example of how this plays out
I've seen versions of this with different buyers, so here's a composite that captures the pattern. A buyer locks her rate 45 days out on an FHA purchase, which sounds like plenty of runway. The appraisal comes back low. The seller needs two weeks to work through a price adjustment. The closing date moves. Her lock expires nine days before the new closing date, and nobody flags it until her loan officer calls to explain the extension fee. The delay wasn't caused by anything she did. The fee still landed on her desk.
What actually happens when a lock expires
Your rate lock agreement has a lock period built in, usually 30 to 60 days from the day you locked. If your loan doesn't fund before that period ends, the lender is no longer obligated to honor your rate. To keep it, you request an extension, and in most cases you pay for it.
The technical layer: your file was priced against market conditions on the day you locked. Once the lock lapses, that pricing lapses with it unless you pay to hold it in place.
What an extension actually costs
The reality is extension fees are smaller than most buyers assume, and also easy to get blindsided by if nobody explains them upfront. Extension fees typically run 0.125% to 0.5% of the loan amount, depending on the lender and how many days you need. On a $400,000 loan, that's roughly $500 to $2,000, not the full percentage point some buyers brace for.
Some lenders charge it as a flat fee rather than a percentage. Some waive it if the delay wasn't your fault, a slow appraiser, a title issue, a seller who needed more time, while charging it if the delay was on your end. It's worth asking your lender which policy they use before you're the one calling to find out.
An extension and a float-down are not the same tool
These get lumped together, and they solve different problems. An extension keeps your existing locked rate alive past its original expiration. A float-down lets you capture a lower rate if the market moves down while you're locked, instead of being stuck at your original number. Float-down usually costs 0.25% to 0.5% of the loan amount, and most lenders require rates to drop by at least a quarter to half a point before you can even use it. If your lender offers both, ask which one applies to your situation rather than assuming they're interchangeable.
Why this matters right now
Freddie Mac's most recent Primary Mortgage Market Survey has the 30-year fixed averaging 6.49% for the week of July 9, 2026, up slightly from 6.43% the week before. That's lower than a year ago, when it averaged 6.72%, but the week-to-week movement has been small. There's no strong signal here that rates are about to drop in a way that makes floating past your lock, or betting on a float-down, worth the risk. If you're locked, the more useful question is whether your timeline has enough buffer to actually close before that lock expires.
What to ask before you lock, not after
A few questions upfront save the surprise later. Ask your lender what the extension fee is and how it's calculated, so you know the number before you need it. Lock for the length of time your transaction realistically needs, not the shortest option offered. Keep your file complete and respond quickly to lender requests, since delays you cause are the ones you're more likely to pay for. And if a float-down is part of your deal, ask what threshold triggers it and how many times you can use it.
None of this is a reason to avoid locking. It's a reason to understand what you signed. A lock protects you from the rate going up. It doesn't protect you from a slow closing, and that gap is exactly where buyers get caught off guard.