Start by saving 15 percent of your salary at age 25 into a 401(k) plan, an IRA, or a taxable account (or all three). Put equal amounts of that 15 percent into just three different mutual funds: A U.S. total stock market index fund An international total stock market index fund A U.S. total bond market index fund. Over time, the three funds will grow at different rates, so once per year you’ll adjust their amounts so that they’re again equal.
