Rate locks: windows, float-downs, and extension math

Between the day your offer is accepted and the day you close, mortgage rates keep moving — and on a $400,000 loan, a quarter-point move changes your payment by about $65 a month and your 30-year interest bill by more than $23,000. A rate lock is the lender's promise to hold your quoted rate for a set window, usually 30, 45, 60, or 90 days. It sounds like free insurance. It isn't. Locks have a price baked into the rate, expiration risk on the back end, and a one-way structure: they protect you if rates rise but strand you at the locked rate if rates fall. Managing the lock well is one of the few parts of the mortgage process where an informed borrower can reliably save four figures.

How lock pricing actually works

Lenders don't charge a separate lock fee for standard windows — they build the cost into the rate sheet. A longer lock means the lender carries interest-rate risk longer, so the rate or the points climb with the window. A typical spread: the 30-day lock is the baseline, a 45-day lock costs roughly 0.125% more in points (about $500 on a $400,000 loan), a 60-day lock costs 0.25%, and a 90-day lock can cost 0.375% or a slightly higher rate. That means picking a 90-day lock 'to be safe' on a deal that will close in 35 days is just donating money.

Picking the window: lock to closing, plus a cushion

The rule is simple: count the days from lock to your realistic closing date, then add a 7–10 day cushion for appraisal delays, underwriting conditions, or a seller who needs to push the date. If your contract says 40 days to close, a 45-day lock is tight and a 60-day lock is defensible if extensions at your lender are expensive. What you're balancing is the known, small cost of a longer window against the unknown, larger cost of an extension bought under duress.

Extensions: the expensive back door

When a lock expires before closing, you don't automatically get the current market rate — you get the worse of a repriced rate or an extension fee. Extensions typically run 0.125% to 0.25% of the loan amount per 7–15 days, and some lenders charge more for a second extension than the first. On a $400,000 loan, a 15-day extension at 0.25% is $1,000 — often more than the entire cost of having chosen the longer lock upfront. Worse, if the lock fully lapses, many lenders reprice you at the higher of the original rate or current market, so you carry the downside of both worlds.

Float-downs: paying for a two-way option

A standard lock protects you from rising rates but locks you out of falling ones. A float-down option converts that into a two-way bet: if rates drop meaningfully before closing, you can reset to the lower rate once. The catch is in the fine print. Most float-downs cost 0.25% to 0.5% of the loan upfront (or a slightly worse starting rate), require rates to fall by a minimum trigger — commonly 0.25% or more — before you can exercise, and often give you only a portion of the drop rather than the full move.

• Ask for the trigger: how far must rates fall before the float-down activates? A 0.375% trigger makes the option nearly worthless in calm markets.
• Ask what you capture: the full new rate, or the new rate plus a margin? 'Market minus nothing' is rare.
• Ask when you can exercise: some lenders allow it any time before docs; others only in a narrow window 7–10 days before closing.
• Ask the cost: an upfront fee is easier to evaluate than a buried rate adjustment. Get both quotes in writing.
• Remember the free alternative: if rates collapse after you close, you can refinance. A float-down is mostly worth paying for when a refinance would be slow or costly for you.

Should you float instead of locking?

Floating — waiting to lock while rates hopefully fall — is a coin flip with asymmetric stakes. Nobody reliably predicts short-term rate moves, including loan officers, and the borrower floating into a Fed meeting or an inflation report is taking event risk they can't hedge. The honest framework: lock when the payment at today's rate is one you're comfortable with, and treat any future drop as a refinance opportunity rather than a missed trade. Float only when you have genuine flexibility — a distant closing, strong reserves, and the ability to absorb a 0.5% rise without stress.

1. 1
   Confirm the timeline

   Get your lender's honest current turn time and your contract closing date before choosing a window.

2. 2
   Price two windows

   Ask for the rate sheet at your realistic window and the next one up. The spread is usually small.

3. 3
   Ask the extension question upfront

   Get the extension fee schedule in writing before you lock — it's the number that decides how much cushion to buy.

4. 4
   Lock with a named expiration

   Get the lock confirmation showing rate, points, and expiration date. Calendar it 10 days early.

5. 5
   Manage the deadline

   If closing slips, push your agent and lender immediately — a 3-day extension negotiated early beats a 15-day one bought late.

The bottom line

Treat the lock as a deliberately purchased option, not paperwork. Match the window to a realistic closing date plus a week of cushion, get the extension fee schedule in writing before you commit, and pay for a float-down only when the trigger and capture terms make it a real option rather than a marketing feature. The borrowers who lose money on locks aren't unlucky — they picked windows on hope, floated into news events, and bought extensions retail. A half hour of questions before locking is worth more than any rate forecast.