Mortgages with a convertible rate feature allow borrowers to move into a fixed rate at any time with no penalty. 

There are also a few 1-year fixed mortgages that can be converted to either a fixed or a variable rate.

When converting, you generally need to choose a new term that is at least as long as the term you have remaining.

Variable-rate and short-term fixed-rate mortgages are commonly offered with a convertible feature.  In the case of variables, you can only convert into a fixed rate.