There's no guaranteed interest rate, since the amount of money homeowners collectively pay back every month is a function of how many have refinanced and how many have defaulted.

没有保证利率，因为金额业主每个月偿还利息是根据再融资和违约的多少来定的。

youdao

They are issued with a fixed, guaranteed rate of interest (currently 3%).

FORBES: Fact and Comment

Then there is life insurance, which at least seems to offer a guaranteed fixed rate of interest, plus a bit more in good years.

ECONOMIST: Not all it should be

Funds that invest in fixed income municipal securities are not guaranteed and are subject to interest rate, inflation, and credit risks.

FORBES: Muni Bond Manager's Journal: Looking For Real Value