No one knows for sure how interest rates will move at any given time, but your lender may be able to give you an estimate of where it thinks mortgage rates are headed. If interest rates are expected to be volatile in the near future, you may want to consider locking your interest rate if rising rates will no longer allow you to qualify for the loan. If your budget can handle a higher loan payment or if the lender's lock fee seems excessive for your means, you might want to consider allowing the interest rate to 'float' until the loan closing.