The payment formula
Principal and interest come from the standard amortization formula M = P × i / (1 − (1 + i)^−n), where P is the total financed balance (home price minus down payment, plus the funding fee), i is the monthly interest rate and n is the number of monthly payments.
Because interest is charged on the remaining balance, the first payment goes almost entirely to interest. On a $326,880 balance at 6.5% — a $320,000 base loan with a $6,880 funding fee — about $1,771 of the first payment is interest and only around $296 reaches the principal.