What Is a Mortgage Rate Lock?
A rate lock freezes your mortgage rate for a set window while your loan closes. How locks, extensions, and float-downs work — and the mistakes that cost real money.
A mortgage rate lock is your lender’s written commitment to honor a specific interest rate for a set period — commonly 30 to 60 days — while your loan gets to closing. Lock, and the market can move all it wants; your rate doesn’t. The catch is the clock: if your closing slips past the lock’s expiration, you’ll pay for an extension or face whatever the market rate is that day.
Why locks exist
Between your offer and your closing sits several weeks of underwriting, appraisal, and escrow. Mortgage rates reprice constantly during that stretch, and on Seattle-sized loans, small moves are not small money: as a rough illustration, a quarter-point swing on a $700,000 loan changes the payment by something on the order of $100 a month — every month, for as long as you hold the loan. Nobody can sign a purchase contract while their largest monthly expense is a moving target, so lenders sell certainty: the rate lock.
And it is, in effect, sold. A lock is priced into your deal — longer locks cost more (in rate or in points) than shorter ones, because the lender is absorbing more market risk on your behalf.
The vocabulary that actually matters
- Lock period. 30, 45, 60 days are typical tiers. Your lock should comfortably cover your contracted closing date, not match it exactly.
- Extension. Closing slipping? Locks can usually be extended for a fee, often quoted as a small fraction of the loan amount per chunk of days. Cheap insurance compared to losing the rate; not free.
- Float-down. Some lenders offer a one-time option to grab a lower rate if the market drops meaningfully after you lock — usually for a fee or a slightly worse starting rate. Worth asking about; rarely worth assuming.
- Lock-and-shop. A pre-contract lock some lenders offer while you’re still house hunting. Useful in rate-volatile stretches, with conditions attached.
- Floating. The alternative to locking: take whatever the rate is when you finally lock later. That’s a market bet, made with your housing payment.
How this plays out in a Washington purchase
Washington deals close through escrow, and the closing date in your purchase contract is the date your lock has to survive to. The classic local failure chain looks like this: appraisal takes longer than hoped, underwriting asks for one more document, the escrow timeline shifts a few days — and a 30-day lock on a 35-day reality expires with the finish line in sight. The buyer then pays extension fees during the most stressful week of the transaction, with zero leverage.
Self-employed buyer? Underwriting takes longer for you; price a longer lock from the start (more on why in our self-employed buyer’s guide).
Common mistakes, briefly
- Locking exactly to the closing date. Buy buffer. A 45-day lock on a 35-day close costs a little; an expired lock costs more.
- Floating out of greed. “Rates might dip before closing” is a coin flip with your payment. Lock when the deal numbers work, and stop watching the ticker.
- Comparing lender quotes with different lock periods. A rate quoted with a 15-day lock will look better than one quoted at 60 days. Make every lender quote the same lock period or the comparison is fiction.
- Forgetting the lock when negotiating repairs. Reopening negotiations after inspection can push the timeline; remember the lock clock is running while you argue over a furnace.
- Confusing a lock with approval. A lock freezes the price of the loan, not its existence. Underwriting can still say no.
What to actually do
Ask every lender three questions in writing: How long is the lock and what does a longer one cost? What does an extension cost per week? Is there a float-down, and on what terms? Then lock for longer than you think you need, calendar the expiration, and model what the rate means in dollars with our mortgage calculator. If you’re weighing locks against other rate strategies, see buydowns and points and fixed vs. ARM.
Rates deserve this much scrutiny — so do agent fees. Manaky Homes shows what Greater Seattle agents actually charge, published side by side, free. Waitlist’s open.
