Mortgage Rate Lock Extension Cost Calculator
Calculate the exact cost of extending your rate lock and compare it against what you would pay if rates rise 0.25%. Get a clear verdict: pay the extension or let the lock expire.
What Is a Mortgage Rate Lock Extension?
A mortgage rate lock guarantees your interest rate for a set period — typically 30, 45, or 60 days from application. If your closing takes longer than expected (appraisal delays, title issues, underwriting backlog), you can pay a fee to extend the lock rather than risk your rate expiring and being replaced by a higher market rate. Extension fees are quoted as a percentage of the loan amount — typically 0.125% to 0.50% depending on the extension length. Last updated: May 2026.
Extension Fee vs Rate Rise Risk Comparison
| Extension Period | Typical Fee | Cost on $400K Loan |
|---|---|---|
| 15 days | 0.125% | $500 |
| 30 days | 0.25% | $1,000 |
| 45 days | 0.375% | $1,500 |
| 60 days | 0.50% | $2,000 |
When Paying the Extension Always Wins
If current market rates are above your locked rate, extending is almost always the right financial decision. A 0.25% higher rate on a 30-year, $400,000 loan adds roughly $58/month — which is $20,880 over 30 years. Compare that against a $1,000 extension fee and the math is clear. The only scenario where letting the lock expire makes sense is if market rates have fallen significantly below your locked rate — in which case you benefit by re-locking at the lower rate (though you'll also pay new lock fees). Always confirm the current market rate with your loan officer before deciding.