Mortgage Rate Lock: How It Works, How Long It Lasts, and When to Lock

Everything you need to know about mortgage rate locks — how they protect you from rate increases, how long locks last, the cost of extending, and the strategic question of when to lock.

A mortgage rate lock protects you from interest rate increases during the period between your loan application and closing. In a volatile rate environment, that protection can be worth thousands of dollars. But locks expire — and an expired lock at the wrong moment can cost you money or delay your closing. Here's everything you need to know.

How a Rate Lock Works

When you lock your mortgage rate, the lender guarantees a specific interest rate for a defined period — regardless of what happens to market rates during that time. If rates rise 0.5% during your lock period, you still get the original locked rate. The lock is typically tied to a specific loan program, loan amount, and property.

Common Lock Periods and Their Costs

• •15-day lock: Cheapest; used for refinances that are close to closing; very tight timeline
• •30-day lock: Most common; appropriate for purchase transactions moving quickly
• •45-day lock: Slightly higher cost; useful for transactions with complex underwriting or title issues
• •60-day lock: Higher cost; used for new construction, delayed closings, or complex files
• •90+ day lock: Available from some lenders for new construction; significantly higher cost

Longer locks cost more because the lender is taking on more risk that rates will move against them. The cost is usually built into a slightly higher rate (not a separate fee) — a 60-day lock might be 0.125–0.25% higher than a 30-day lock on the same day.

What Happens If Your Rate Lock Expires?

If your loan doesn't close before the lock expires, you have two options: extend the lock or let it expire and renegotiate at current market rates.

• •Lock extension: Typically costs 0.125–0.375% of the loan amount per 15-day extension. On a $400,000 loan, extending a lock by 15 days might cost $500–$1,500.
• •Renegotiation: If rates fell during your original lock period, expiring and relocking at a lower rate might be beneficial. If rates rose, this is painful.
• •Whose fault is the delay matters: If the delay was caused by the lender (slow underwriting), they may extend your lock at no cost. If it was caused by the buyer's delayed documents, the buyer typically pays.

Float vs. Lock: The Strategic Decision

Before locking, many borrowers wonder: should I float (wait to lock) hoping rates fall, or lock now and get certainty? This is genuinely difficult to predict, but here's a framework:

Arguments for locking now:

• •Rate certainty for budgeting — you know exactly what your payment will be
• •You're close to qualifying and a rate increase would push you over your DTI limit
• •Economic data suggests rates are more likely to rise than fall
• •The difference between where rates might go is small relative to the cost of anxiety

Arguments for floating:

• •Economic data or Fed signals suggest rate cuts are imminent
• •You have significant cushion in your DTI and can absorb a slightly higher rate
• •Rates have been trending downward and the momentum looks sustainable

Float-Down Options

Some lenders offer a float-down option: you lock your rate but reserve the right to drop to a lower rate if rates fall by more than a specified amount (usually 0.25–0.5%) before closing. Float-down options cost money (typically 0.125–0.25% of the loan amount) and have conditions. They give you some upside potential while maintaining rate protection — but evaluate the cost carefully.

The Lock Timeline for a Typical Purchase

1. 1Day 1: Purchase contract signed — this is when most lenders allow you to lock
2. 2Days 1–3: Submit formal loan application, receive Loan Estimate
3. 3Days 1–7: Decide to lock or float based on market conditions and your timeline
4. 4Days 15–30: Appraisal completed, underwriting begins
5. 5Days 25–40: Conditional approval, provide additional documents
6. 6Days 28–45: Clear to close
7. 7Days 30–45: Closing — lock should still be active

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