Most first-time buyers learn about rate locks the day their loan officer asks "do you want to lock?" and offers about thirty seconds to decide. The decision is small in dollar terms compared to home price or down payment, but it's one of the few financial choices in the mortgage process that's almost entirely reversible-in-one-direction. Lock too early and rates fall, you're stuck paying more. Lock too late and rates rise, you're paying more. Understanding what's actually happening helps you make the call when it comes up.
What a rate lock actually is
A rate lock is a contractual commitment from your lender that the interest rate they're quoting today will be the rate on your loan when it closes — as long as it closes within a defined lock period. The most common lock durations are 30, 45, and 60 days. Longer locks (90, 120, even 180 days) exist for new construction or other special cases. Shorter locks (15 days) exist for fast-closing scenarios.
The mechanics on the lender's side: when you lock, the lender effectively reserves a mortgage-backed security position in the secondary market that matches your loan's parameters. If rates rise between today and your closing, the lender absorbs the difference — they sell your loan into the secondary market at the rate you locked, even if the market rate is higher by then. If rates fall, the lender keeps the difference — they sell your loan at your higher locked rate while market rates have moved lower.
This is why rate locks aren't free. The lender is taking on price risk in exchange for charging a slightly higher rate than they'd charge without the lock. The cost of the lock is baked into the rate you're quoted; the longer the lock, the higher the rate.
What lock duration actually costs
Lock-period costs are usually expressed as differences in rate or in pricing points. The cost varies by lender, market environment, and loan type, but the general pattern is consistent: each additional 15 days of lock duration costs roughly 0.04 to 0.10 percentage points on the rate, or 0.125 to 0.375 points in upfront cost.
Representative example on a $400,000 conventional 30-year loan at current rates (May 2026):
| Lock duration | Typical rate premium | Monthly P&I impact | Lifetime interest impact |
|---|---|---|---|
| 15-day lock | -0.04 pp (cheaper) | −$10 / month | −$3,500 |
| 30-day lock | baseline (e.g., 6.37%) | $0 | $0 |
| 45-day lock | +0.05 pp | +$13 / month | +$4,700 |
| 60-day lock | +0.10 pp | +$26 / month | +$9,400 |
| 90-day lock | +0.20 pp | +$51 / month | +$18,700 |
These are illustrative — actual lock pricing varies by lender and changes weekly with market volatility. In high-volatility environments (high MOVE Index), lock premiums widen because the lender's price risk is larger. In calm markets, the premiums tighten. Some lenders charge for locks as basis points on the rate; others charge as points (upfront dollars). The math works out similarly either way.
The practical takeaway: pick the shortest lock that gets you reliably to closing. A 30-day lock is the default for purchase transactions because most well-organized purchase contracts close in 30 days from contract acceptance. If your purchase timeline is longer (new construction, complicated title, contingency-heavy contract), get the longer lock from the start rather than paying for a lock extension later.
Lock extensions — much more expensive
If your loan doesn't close before your lock expires, you'll need to extend or re-lock. Lock extensions are priced punitively — typically 0.125 to 0.5 points (in upfront cost) per 15 days of extension, sometimes more. Re-locking entirely puts you at current market rates, which may be much worse than what you originally locked.
The implication: lock extensions are a serious tax on closing-day delays. The way to avoid the tax is to either (a) pick a lock period that includes a safety buffer for the kind of delay your transaction is prone to, or (b) work the closing process aggressively to avoid delays. The most common reasons for closing slip past the lock: appraisal delays, title issues discovered late, income or asset documentation requests that pile up, and contingency negotiations.
When to lock during the process
You typically have the option to lock anywhere from the start of the application process to as late as a few days before closing. The two extremes:
Lock immediately on application. You get rate certainty for the entire process. If rates rise, you're protected. If rates fall, you don't benefit (unless your lender offers float-down — more below). This is the right choice when rates have been trending up, when you're worried about further rate increases, or when your budget is tight enough that a 0.25-point rate increase would change the deal.
Float to closer to closing. You don't lock until you're closer to a closing date. If rates fall before you lock, you benefit. If rates rise, you pay more. The case for floating is strongest when rates have been trending down, when the market environment is calm, and when you have budget flexibility to absorb a small rate increase if floating doesn't go your way.
Most experienced loan officers lock at the point in the process where the marginal benefit of further floating is small relative to the risk. For a typical 30-day purchase transaction, that's often within the first 7-14 days of application — early enough to capture most of the rate certainty benefit, late enough to absorb any small market moves that happen between application and rate-sheet posting on the lock day.
Float-down provisions, honestly assessed
A float-down provision lets you lock in a rate today and then "reset" to a lower rate if market rates drop materially before closing. This sounds great. It's also typically less valuable than it looks, for three reasons.
Float-down isn't free. It's priced into the lock — usually 0.125 to 0.375 points (upfront cost), or 0.05 to 0.10 percentage points on the rate. So you're paying for the option whether or not you end up using it.
Float-down has trigger thresholds. Most float-down provisions don't activate unless rates drop by some minimum amount — typically 0.25 to 0.5 percentage points below your locked rate. Smaller rate drops don't qualify. So if you lock at 6.50%, rates drop to 6.35%, your float-down doesn't trigger and you're stuck at 6.50% having paid for the option.
Float-down has timing windows. Most provisions can only be exercised within a specific window (often 7-15 days before closing). If rates drop dramatically two weeks after you lock but recover before the exercise window opens, you don't capture the benefit.
The math: if you pay 0.125 points for a float-down on a $400,000 loan, you're paying $500 upfront for the option. The option pays off only if rates drop more than 0.25-0.5 percentage points during a specific window, and even then only by the difference between the original lock and the new rate, capped at some maximum. For most borrowers in most market environments, the expected value of the float-down is less than its cost.
When float-down is worth considering: high-volatility markets, longer locks (60+ days), and situations where you're locking at a clearly elevated rate level that you expect might normalize. In stable or trending-up markets, the option is rarely worth the cost.
When rates move during your lock period
Once you lock, your rate is fixed regardless of what the market does. Two scenarios worth thinking about:
Rates rise materially after you lock. You're protected by the lock — your loan closes at your locked rate even though market rates are higher. This is the upside of the lock you paid for. No action required.
Rates fall materially after you lock. Two paths. If you have a float-down provision that triggers, you may be able to capture some of the rate drop. If you don't, you have three options: (1) close at your locked rate and refinance later if rates stay lower; (2) ask your lender to re-lock at the lower rate (most won't do this without significant cost — they're already on the hook for your original lock); (3) walk away from your lender and start over with a new lender at lower rates (this resets your appraisal, requires fresh credit checks, may delay closing past your purchase contract deadlines, and forfeits any application fees you've paid).
Option 1 — close at the locked rate and refinance later — is usually the right choice for material drops (0.5+ percentage points). The Refinance vs. Keep calculator shows the break-even math on any specific scenario.
Locking when shopping multiple lenders
Rate shopping across 3-4 lenders within a short window (the credit bureaus treat all credit inquiries within ~14-45 days as a single shopping event for FICO purposes) is the right strategy and the flagship lender guide covers it in depth. The lock question gets complicated when shopping:
You can't lock with multiple lenders simultaneously without unwinding most of them. Each lender holds your lock in their pipeline; closing with one means walking away from the others, forfeiting any application fees or earnest fees you've put down.
The practical sequence: get Loan Estimates from 3-4 lenders on the same day, pick a winner based on the apples-to-apples rate and fee comparison, then lock with that lender. Don't lock with anyone until you've made the decision.
Some borrowers try to negotiate by getting LEs from multiple lenders and asking each to match the best one. This works occasionally — some lenders will price-match a competitor's quote — but it's not universally effective. Most loan officers have limited authority to discount below their initial quote, and the time spent re-negotiating may be better spent just picking the best original quote.
Lock-decision checklist
When the loan officer asks "do you want to lock?", these are the questions worth asking before answering:
- What's the rate, and what's the lock duration? Get both numbers explicitly. A 60-day lock at 6.45% is materially different from a 30-day lock at 6.40%.
- What's the cost of extending the lock if my closing slips? Get the extension pricing in writing before you lock. This is the cost you'll pay if anything goes wrong with the closing timeline.
- Is there a float-down option, and what does it cost? Get the trigger threshold, exercise window, and cost explicitly. Decide based on the math, not the brochure.
- What's the current rate environment doing? Check the 10-year Treasury yield trend over the past 2-4 weeks. If it's been rising, lean toward locking sooner. If it's been falling steadily, the case for floating is stronger.
- How tight is my budget on this house? If a 0.25-point rate increase would change your affordability, lock now and don't gamble. Risk avoidance is worth real money when your margin is thin.
The honest meta-rule: nobody, including the loan officer, knows what rates will do over the next 30-60 days. The professionals make educated guesses based on patterns; they're frequently wrong. Lock decisions are about risk tolerance, not market timing.