Mortgage notes usually carry a
grace period, 15 days is typical but some are as short as 10 days. Many people "play the float" that is, delay through most of the grace period before making payment, and no one, including the
lender thinks very much about it.
On day 16, however, a late fee is assessed. At this point there are no ramifications beyond that late fee and maybe a "friendly reminder" call from the lender's customer service department. The late payment probably won't even show up on the borrower's
credit report. On
Day 30 that changes. At that point the borrower is in default and things quickly turn serious and the foreclosure process speeds up.
Starting on
day 16, additional debt is incurred in the form of the
mortgage late fee - usually a percentage of the principal balance; three percent is typical which, on a $300,000 mortgage is plus or minus a $100 penalty and, if the next payment and the next are also missed, the cost of bringing the mortgage current grows pretty fast.
Past
day 30, some lenders will allow a borrower to make a partial payment of the past due amount; others will insist that everything be brought current; lenders may even return a check if it does not cover both the current and the past due payments and maybe the late charges as well.