“Do you want a lock?”

That may seem like a logical question for your insurance agent to pose, but you can expect it from your mortgage lender, too.

He’s not asking about bolting your door but rather if you want to secure your mortgage rate.

Interest rates fluctuate, influenced by economic trends. So, conceivably, the rate that’s prevailing when your lender calls to say the mortgage you need to buy your new home is approved, might be one-half a percent different when you actually take the loan at closing of the sale 45 days later. If the rate move is higher, that’s going to hurt, because you’ll be facing higher monthly mortgage bills.

The ability to “lock” or guarantee that the rate when you’re approved is the rate you receive can be worthwhile for those jittery about rate rises.

But, once you do lock, “It’s like marriage – it’s [your rate] for better or worse, the closer you get to closing,” notes Charles Chedester, vice president of the Iowa Association of Mortgage Brokers. The “worse” he refers to is if rates fall below what you locked in at – you’re still getting the locked rate.

However, if there’s time before closing, a lender may be able to re-lock, and there may be locks with a “float-down” option, adds Shane Marzullo, chairman of the Ohio Association of Mortgage Professionals.

Given that rates have been “low and stable” many borrowers don’t want to lock – especially since locks for more than 30 days typically cost a couple of hundred dollars or more, adds Keith Gumbinger, of mortgage data firm HSH Associates.

So it comes down to this: If you like the rate you’re quoted enough to “marry” it, you’ll want to lock.