The safest way to make your retirement savings last

Willie Grace | 4/1/2015, 2:20 p.m.
In theory, it should be pretty simple to do exactly what you describe. And there are plenty of financial advisers ...
It's easy to live for the moment and leave planning the future to another time. But when it comes to planning for your retirement, it is never too early.

NEW YORK (CNNMoney) -- Whenever I read about annuities, I wonder why you can't create one on your own without an insurance company. Just invest your money conservatively and then watch your expenses so you don't blow through your savings too soon. Wouldn't that plan work just as well, if not better, than an annuity? --Mike J., New Jersey

In theory, it should be pretty simple to do exactly what you describe. And there are plenty of financial advisers more than happy to carry out such a plan for people who don't like the idea of buying an annuity, but aren't confident enough about their investing skills to carry out your plan on their own.

But creating income for life that's as reliable as what you would get from a pension or an annuity isn't as easy as it may seem. In fact, there are some elements of an immediate annuity -- aka an income annuity --that you simply can't duplicate. Which makes it virtually impossible to match an annuity's lifetime payments investing on your own, unless you take on more investing risk.

Here's an example.

Let's say you're a 65-old-man who has $100,000 from which you would like to draw a stable and reliable income for the rest of your life. If you go to an immediate annuity calculator, you'll find that at today's interest rates, forking over $100,000 to an insurer would provide guaranteed lifetime payments of about $540 a month for a man that age. (Payments would be a bit lower for a 65-year-old woman, as women generally live longer.)

So the question is, could you generate the same or higher monthly income investing on your own?

Since you don't want to run the risk of incurring investment losses that could deplete your savings too soon, you'll want to stick to a pretty secure investment, say, 10-year Treasury bonds, which recently yielded about 2% annually. If you put that $100,000 into 10-year Treasuries yielding 2% and withdraw $540 each month, your hundred grand would last about 18 years, which means you would go through your savings by age 83.

That's a problem, since the Society of Actuaries estimates that a 65-year-old man has a life expectancy of 86 to 87, while the life expectancy of a woman the same age is 88 to 89. And many people will live well beyond their life expectancy. In short, you have a very good chance of running out of money before you run out of time.

So why not just invest for a higher return?

At a 4% annual return your dough would run out in 24 years, taking you to age 89. At 5%, it would last almost 29 years, taking you to age 94. But the higher the return you shoot for, the more risk you take and the more volatile your returns are likely to be. If you run into a market setback or string of subpar returns, your savings could run out years sooner than projected. You can see the probability that your money will last given different mixes of stocks and bonds by going to this retirement income calculator.