A first lien or first mortgage is the primary loan that pays for a property. The loan has priority over all other liens or claims on a property in the event of default.

If the loan-to-value (LTV) ratio of a first mortgage is greater than 80%, lenders generally require private mortgage insurance (PMI). In such a case, it can sometimes be economical for a borrower to limit the size of the first mortgage to 80% LTV and use secondary financing to borrow the remaining amount needed.