Target date funds make retirement investing easy, but their biggest flaw is how little they know. They see only your retirement year, not your Social Security timing, pension, spending needs, risk tolerance, spouse's assets or other holdings. Two people retiring the same year can need very different portfolios yet own the identical fund. Critics also point to glide paths that cut stock exposure sharply near age 60 even though people now live longer, and to concentration in large cap stocks after years of market dominance. Funds are not all alike either, with different glide paths, underlying holdings and fees, and the difference between "to" and "through" designs is easy to miss. The takeaway is not to abandon them. For hands off savers they can work well, especially when costs are low and disclosures are clear. Everyone else should check the stock and bond mix at key ages, compare it with their full picture and make a deliberate choice about retirement income.

Finsum: The smartest target date investors will look under the hood as retirement nears and make sure the glide path fits their life.