A lock is insurance with a price built into your rate. Here is how to work out whether the window you are buying matches the closing you actually have.
A rate lock freezes your rate for a set window while the file closes. Common windows are 30, 45 and 60 days. Longer windows cost more, and the cost is usually not a separate fee: it is built into the rate itself, which is why a 60 day lock prices slightly above a 30 day lock on the same file.
So the question is not whether to lock. It is which window to buy. Buy too short and you pay to extend, typically per day. Buy too long and you paid for coverage you never used. Either way the money is gone.
Match the window to the file, not to the calendar. A purchase with an accepted offer, a scheduled appraisal and a complete document package rarely needs the longest window. A new construction closing with a completion date that is an estimate rather than a date needs the long window and probably an extension policy agreed in advance.
Two structures are worth asking about explicitly. A float down gives you one chance to reset lower if the market moves meaningfully in your favour before closing, usually in exchange for a slightly higher starting rate. An extension policy tells you in advance what a delay costs per day. Get both in writing at lock, not at day 44.
The honest framing is this. Locking is not a forecast, and treating it as one turns your housing costs into a speculative position. If the payment works at the rate available today, the certainty is usually worth more than the possible saving.
Illustrative sample figures for a template demonstration. Not a rate quote, not an offer to lend, and not live market data.
