4.499 with a buy down cost of .375% or $721.65. P&I payment is $974.97
...
3.99% with a buy down cost of 1.625% or $3,127.19. P&I payment is $918.64.
Savings per month 974.97-918.64 = $ 56.33 / month
Expense: 3127.19-721.65 = $ 2405.54
Breakeven period = 2405.54 / 56.33 = 42.7 month = 3 years and 8 month.