In the USA, the usual mortgage has a fixed interest rate for the term of the mortgage. In New Zealand the interest rate is approximately a floating (edit:variable) rate over the 30 year period.
In NZ the mortgage interest rate (which controls your repayments) can be fixed for up to 5 years (the median is 2) but after the “fixed” period the interest rate resets to the current interest rates (edit: typically mortgagees lock in a new 2 year “fixed” rate at the current 2 year interest rate). NZ rates were around 2% to 3% since 2008 [1], but now they are closer to 6% [2] and most mortgage holders in New Zealand will have to pay twice as much for the interest component of their mortgage repayment, putting some people under financial stress (an acquaintance is being forced to sell an investment property because they were over-leveraged). The mortgage interest rate over the 30 year term is more of a stepwise approximation to the floating interest rate: I am unsure how much control the mortgage holder has over varying the principal repayments (I think I can pay 20% more principal per payment, shortening 30 year term to 24 years).
It is more complicated than that, and the USA has a wide variety of mortgage products you can buy including ones similar to NZ (not just the usual USA fixed rate 30 year). Other countries have their own quirks, so I am only speaking for NZ where I understand the details better.
