The average monthly savings for this group of candidates is $268, for a total aggregate of $2.99B per month. Sources other than Freddie Mac PMMS are showing rates even lower, which means the number of refi candidates could actually be larger.
Furthermore, in Q4 2019, approximately 76% of homeowners were either able to keep their interest rate the same or, in many cases, significantly decrease their interest rate through cash-out refinancing, the largest such share since Q4 2016. This includes 50% who decreased their interest rate by at least 0.50% and 25% who decreased their interest rate by 1% or more.
Much more detail can be found in Black Knight’s January 2020 Mortgage Monitor Report.