The lender will likely impose a late charge and it may be reflected on your credit report. Most lenders will give you a grace period after your monthly due date before they impose a late charge. If you are repeatedly late with payments, you may have trouble refinancing your loan should you choose to do so. If you stop making payments completely, your lender can start foreclosure proceedings and you could lose your house.

If you forgot to mail in your check, or the check was lost in the mail and this was the first time- call your lender immediately. They may give you the benefit of the doubt, and not penalize you.