For example, if you earned $70,000 and consistently saved 15% per year in a low-cost S&P 500 index fund — which has averaged about 10.4% annual returns since 1957 — you could save double your income in around nine years and 7x your income in about 18 years.Fidelity recommends having 2x your salary by age 35, 4x by 45 and 7x by 55. To hit these milestones, they suggest investing 15% of your pretax income into a diversified portfolio focused on growth and income.The median salary for someone aged 55 to 64 is ...