"Until I have all the pieces to the puzzle," Cook says, "I can't accurately quote what their rate and cost will be."
How long can a rate be floated?
In theory, a mortgage rate could be floated until the transaction closes. But that's not practical in the real world, explains Peter Thompson, a senior loan officer at Prospect Mortgage in Naperville, Illinois.
Instead, the rate must be locked at least a few days or more, likely a week before closing to allow time for the lender to prepare disclosures and loan documents. This paperwork is known as the closing package.
"Typically, you want a week between locking and closing," Thompson says. "You can't really (float until) the day before because we have to do the closing package."
How much does a rate lock cost?
Borrowers are often told there's no charge for a rate lock. That's true in the sense that the rate lock isn't associated with a fee. But a rate lock isn't free. Rather, a longer rate lock typically involves a higher interest rate, which is more expensive for the borrower. The interest rate or "pricing" difference between a 15-day rate lock and 60-day rate lock might be as little as one-eighth or as much as half of a percentage point, Thompson explains.
"The shorter the term that it's locked, the more risk (the borrower) is taking on," he says. "But they should be getting a better price."
What happens if the rate lock expires before closing?
The lender might offer to extend the rate lock. If not, that combination of rate and points might no longer be available.
"If you go beyond the lock period," Thompson says, "you'll have to get an extension, or if an extension isn't possible, you'll end up paying the market rate, and it could be higher."
This back-end risk is a good argument for a longer rate lock, especially if the transaction involves a short sale or a brand-new home that's under construction.
"The big thing is having a firm knowledge of when you'll be able to close," Thompson says.