So I went to the investor.gov website and got to playing around with one of their compound interest calculators and entered the following: A =$1000, PMT=$150(monthly), t=45 years, r=8%, and it's being compounded monthly. The calculator said the future value would be $827,344.58 I would like to know what formula was used to get this result and how does the calculator know when I will make my deposit? Beginning of the month or end of the month? Any help figuring out how the calculator got this answer would be appreciated! Thanks!