If you want to retire by age 65, you should be setting aside 10-17 percent of your income. If you wait until 35 to start, you have to save 15 to 20 percent of your income to retire by 65. The Center determined those ranges by looking at two different projections — one from the Boston College Center for Retirement Research and one from consulting firm Aon Hewitt — that considered factors such as the rate of return on investments, salary growth, life expectancy and Social Security benefits.