What type of mortgage loan is likely to be tied to a publicly available index that is mutually acceptable to the lender and the borrower?

A renegotiable rate mortgage involves a fixed interest rate for a set period, after which the rate can be renegotiated. This type does not directly tie the interest rate to a publicly available index, but rather relies on the agreement between the lender and borrower at the time of renegotiation.

A graduated payment mortgage features a schedule of increasing payments over time, typically designed for borrowers whose income is expected to rise. This type of mortgage does not use an index to adjust rates; instead, it follows a predetermined payment structure, which does not reflect current market conditions.

Freddie Mac is a government-sponsored enterprise that facilitates mortgage financing by purchasing loans and providing liquidity to lenders. It is not a type of mortgage itself, but rather an organization that influences mortgage markets. Thus, it does not involve a publicly available index tied to interest rates in the same way that adjustable rate mortgages do.