Buying
What Is a Mortgage Rate Lock?
By David Golovin · September 9, 2026 · 3 min read
A mortgage rate lock is a lender’s written commitment to hold your interest rate steady for a defined period while your loan processes and closes. If rates go up during that window, you are protected. If rates go down, you stay at the locked rate unless you added a float-down option.
How it works
You request a lock after signing a purchase contract. Close before it expires and you get that rate no matter what the market does. Run long and you pay to extend.
| Lock period | Typical cost |
|---|---|
| 30 days | Free or included |
| 45 days | Free or small fee |
| 60 days | 0.1-0.25% of loan |
| 90 days | 0.25-0.5% of loan |
Float-down options
For an extra fee, a float-down lets you capture a rate drop after locking, up to a cap. Most require a minimum drop before it kicks in.
Rate locks vs. assumable mortgages
A lock protects the rate you got today. An assumption replaces it: you inherit the seller’s existing rate. Roots shows homes with assumable FHA and VA loans, many in the 2-3% range.
FAQ
When should I lock my mortgage rate?
Most lenders let you lock once you have a signed purchase contract. Lock as soon as you are confident about the property and the loan terms. In a rising rate environment, earlier is generally better.
What happens if my rate lock expires before closing?
You have a few options: pay to extend the lock (usually 0.1-0.25% of the loan for each additional 30 days), let it expire and float to the current market rate, or in some cases negotiate with the lender. Ask about extension policies before you lock.
Can I get a lower rate if rates drop after I lock?
Only if you locked a float-down option, which lets you capture a rate decrease up to a specified amount. It typically costs extra. Without a float-down, you are locked at your original rate even if the market improves.
Does an assumable mortgage need a rate lock?
No. When you assume a loan, you inherit the seller’s existing rate. There is no new origination and no rate to lock. You apply to take over the loan, and the rate is whatever the seller already has.