While I like the idea of increasing your bond portfolio over time, I think that a simple rule like ‘hold your age in bonds’ (or the similar, 120-your age = percent you should have in stocks) has some problems. When you’re young (in your twenties or so) it suggests you should have a substantial portion in bonds, even when you have decades to go before you will need your money. On the other end, it suggests you need almost no stock exposure in late retirement, even though people are living past 100 every day. (To say nothing of having funds for your children and others to inherit.)

Something a bit more complex, like ‘Add ten percent bond exposure to your portfolio every decade from age 30 to 60′ is much less quotable, but would be more accurate for what you should really do.