What should your monthly contribution be if your goal is to have $400,000 in your retirement savings account after 50 years. Suppose your APR is 5.4%, and is compounded monthly and that contributions are made at the end of each month, including last month.
I believe this describes an 'ordinary' annuity with payments at the end of the month
months = 50 yrs x 12 = 600 months
monthly interest = .054 / 12 = .0045 % /mo
FV = 400,000
FV = P [ ((1+i)^n-1)/i ) 400000 = P (1.0045)^600 -1)/.0045 results in P = $130.53 / mo