The new loan balance is limited by the math formula of (Current Principal Balance + Upfront Mortgage Insurance Premium). (cahomeloanpro.com)
Interest, calculated using the simple interest formula (current principal balance times the per diem rate) is NOT added to the principal balance. (vertex42.com)
NOTE: Depending on the type of loan and how you postpone your payments, interest may continue to accrue during these periods and unpaid interest will capitalize (be added to your current principal balance) when your account status changes. (myfedloan.org)