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.
Frequently Asked Questions
How much does a mortgage rate lock extension cost?
Extension fees vary by lender and extension length. Typical costs: 15-day extension = 0.125–0.25% of loan amount; 30-day extension = 0.25–0.375%; 45-day extension = 0.375–0.50%; 60-day extension = 0.50–0.75%. On a $400,000 loan, a 30-day extension might cost $1,000–$1,500.
When should I pay for a rate lock extension?
Pay for the extension if the locked rate is meaningfully below current market rates. If market rates have risen 0.25%+ since you locked, the extension cost is almost always worth it — a 0.25% higher rate on a 30-year loan adds roughly $15–$20/month per $100,000 borrowed, totaling thousands over the life of the loan.
Who pays for the rate lock extension?
Typically the borrower pays. However, if the delay was caused by the lender (appraisal backlog, underwriting delay), negotiate to have the lender absorb the extension cost. If the delay was caused by the seller or title company, some buyers request the seller cover the cost as a concession.
Can I float down my rate during a lock extension?
Only if your original lock included a float-down option (typically costs 0.10–0.25% upfront). Without a float-down provision, your rate is fixed during the lock period. Some lenders offer float-downs as a free feature to attract business — ask upfront before locking.
What happens if my rate lock expires?
If your lock expires without extension or closing, you lose the locked rate and must accept the current market rate. In a rising-rate environment, this can be very costly. Always build a buffer — if your expected close is 30 days away, lock for 45 days. Extensions are cheaper than losing a favorable rate.