Based on the number of years until your retirement, calculate the monthly savings required to build a portfolio of $500,000. Assume you are starting with zero savings, can earn 6 percent a year, and that you start saving on the first of each month. What if you could earn 9 percent a year but wanted to save $750,000 what would you need to deposit into savings monthly? My current age is 55 years old. I have 20 years before retirement.