What a lock is
A rate lock freezes your interest rate for a set window - usually 30, 45, or 60 days - while your loan closes. Without one, your rate floats with the market until shortly before closing. The lock is a commitment on both sides: the lender honors the rate even if the market rises.
When to lock
Lock when you are under contract and the payment available today works. Trying to time the bottom of a rate cycle with your family home is speculation carried out with your housing costs. If the payment works, the certainty is usually worth more than the possible saving.
Float-downs and extensions
Some locks include a float-down: if rates drop meaningfully before closing, you get one chance to re-set lower, typically for a fee or a slightly higher starting rate. Extensions cost money per day - another reason fast document turnaround protects your wallet.
After you close
A lock is not a life sentence. If rates fall substantially after you buy, a refinance captures the improvement, subject to its own closing costs and its own break-even. Set a reminder to re-run that arithmetic once a year, and run it against your remaining term rather than against a fresh thirty years.
What to take away
- Lock when the payment works - certainty beats speculation.
- Float-downs exist but are priced in; ask for terms up front.
- Slow documents cause paid extensions.
- Refinancing later is the real float-down.
Illustrative sample figures for a template demonstration. Not a rate quote, not an offer to lend, and not live market data.