On what day of month are home mortgage payments usually due and when late?

There's no specific answer to your question except "check your mortgage statement."  It's reasonable to expect that a payment is due on or about the first of the month. Many mortgage lenders don't consider a mortgage payment "late" (where a late fee is charged) for up to 15 days past the due date.  Late payments beyond 30-days overdue are usually reported to a credit bureau and can start to damage your credit score, so you'll want to avoid this if you can.  If you are struggling making payments on a one-time or short-term basis, you should be proactive, making contact with your servicer to mitigate any damage to your credit. If you are having persistent trouble, you might consider a loan modification.