Depends on your lenders policies, but most banks would let you re-lock at what is called "worst-case" pricing. So, you should be able to let your lock expire, but since current rates are better, you only get to re-lock at your old rate - not the new improved rates....hence "worst-case". WHY? 1) because they can 2) because otherwise you might NEVER close, always looking for a better rate. The banks production needs to be stable. The good news is that you don't have to pay any "re-lock" fees, and your rate is not going up. NOW, be absolutely sure that your rate is higher than current market, because when you let it expire, you will be floating for a minimum of 1 day overnight. This is something that should be covered in detail with your LO.