Great question. It's a lot like a target date fund, but you actually want your fund a lot more personalized. E.g. a man or a woman both 70 years old today would be in the same 2015 target date fund, but she's going to live longer and so has a longer time horizon and should be one or two percent more in equities maybe. But this also varies based on whether you have equity in your home as a cushion, have long term care insurance (which pushes financial needs sooner), are married (especially to someone older or younger), have a separate tax-advantaged account (that should be spent later, typically, meaning you actually have a very short horizon on your non-tax-advantaged account), etc.

The point is, you'd be surprised how different two people are in terms of investment needs even if they retired the same year.

As an aside, we model our investment model most closely after target date funds and annuities. Annuities offer a guarantee (subject to to the insurance company's solvency) but high fees and low flexibility, while target date funds offer good market participation and low fees but don't have the guarantee component. We include a similar blend of securities as a target date fund might, but also include an annuity component for the guarantee.