There are 12 months in a year, so to calculate the total number of months in 4 years, you just need to multiply 12 by 4, which gives you 48 months. I've done this calculation a few times before, and it's always helpful to double-check, but it's pretty straightforward - 12 months per year, times 4 years, equals 48 months, so you should be good to go with that number.