04/04/2012 05:22 pm ET Updated Jun 04, 2012

"4% Rule" Serves as Guideline for Today's Retirees, But Use With Caution

An estimated 10,000 baby boomers turn age 65 each day. Many of them have a significant portion of their retirement savings invested in non-guaranteed defined contribution plans such as 401(k)s and IRAs. As they retire, they will need to switch from saving to spending down. This is a huge shift in attitude and in tactics, and presents a challenge to a new generation of retirees not necessarily prepared to manage a large sum of money and make it last for the rest of their lives.

In the mid-1990s, financial advisor William Bengen researched the question of how much can be taken from a retirement portfolio so a client doesn't run out of money. He created the so-called "4% rule," which says if you withdraw four percent of your initial retirement portfolio plus inflation annually, your portfolio is likely to last 30 years.

I like the four percent rule because it's simple. Most retirees I work with don't want to start a new career learning how to create a retirement paycheck. They want to create the paycheck and get on with the more fun and interesting aspects of their post-earning lives. The four percent rule helps people quickly decide when they'll be able to retire and maintain their standard of living.

For example, if you plan to spend $50,000 per year in addition to your expected fixed sources of income (Social Security, pensions and annuity income), you'll need a portfolio of $1.25 million (50,000/.04) to retire today. If you have $1 million in the bank, it's clear you're going to need to make adjustments to your lifestyle and/or retirement plans.

It's important to note the four-percent rule has drawbacks typically found with simple rules of thumb: there are lots of possible exceptions. One consideration is taxation.

The U.S. tax code is complicated, and it doesn't get any simpler just because you stop getting a W-2. Withdrawals made under the four-percent rule have to allow for taxes. Many pre-retirees aren't familiar with the ins and outs of taxes in retirement, such as the taxation of Social Security at higher adjusted gross income levels, the taxation on required minimum distribution withdrawals from qualified plans or if/how their state will tax their retirement income.

Another consideration is how to invest and withdraw from a large lump sum investment. The four percent rule gives guidance on the "what," but now the "how." Research done since Bengen's first paper tested various combinations of stocks, bonds, and other asset classes to see which combination of assets gives the most confidence for success. Variations of the four percent rule held up in this research.

Alternative strategies to the four percent rule use a "bucket" approach to ensure that enough cash is held over some time period, perhaps 1-3 years, allowing the retiree to decide whether/when to sell assets based on the investment environment. This reduced the risk of retirees having to sell assets to support their spending at a time when the market is experiencing lows.

I prefer this second approach to portfolio management for retirees based on my past work as an asset-liability management actuary. I find "bucket" strategies are similar to cash flow matching, a relatively straightforward asset-liability management technique.

Individuals who don't feel comfortable designing a strategy to draw down retirement assets should consult with a financial advisor who focuses on this area of financial planning and investment management.

The Society of Actuaries recently published a series of Managing Retirement Decisions briefs to educate people nearing retirement, and provide useful information to professionals who work with clients approaching retirement. All 11 briefs, including one on designing a monthly paycheck for retirement, can be found here.