1st lien trust deeds (1st mortgage) are due on the first of each month. Your Truth In Lending Statement will have wording like this: “If you are more than 15 days late you may be subject to a late fee of up to 5%.” This is what usually causes this question to come up. That and your bill that comes to you monthly usually has the amount do on the 1st of the month, and then a different amount that is due if paid on the 16th (or later.)
If you go past the 1st of the following month then you will be more than 30 days late and the lender is required to report you as such. It is important to note that after the 16th the higher amount must be paid prior to the first of the following month.
If you are having trouble paying on time or making the full payment at once you may check into by-weekly or bi-monthly payment plans that most lenders offer as a courtesy to people who are paid weekly or bi-monthly. Hope that helps!