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Here's a pop quiz. Imagine you walk into a financial planner's office and the planner says she would like to run a Monte Carlo simulation on your money-say, the savings and investments you plan to retire on. Do you: A) Suggest the planner contact Gamblers Anonymous? B) Call the police to report a robbery in progress? C) Exit the office as quickly as possible? Or D) Tell her exactly what your assets are and let her spin the big wheel? Strange as it may seem, the correct answer is D. Monte Carlo simulations are one of the best tools financial planners have to help people determine whether their retirement nest eggs are likely to last for the duration of their retirement.
A Monte Carlo simulation is not a roulette wheel stashed in the back of the financial planner's office, though it is named after the famous Monaco casino. The name has more to do with the sense of humor of one of Monte Carlo's inventors-the Polish scientist Stanislaw Ulam, who worked on the Manhattan Project to develop the atomic bomb-than with any resemblance between it and gambling. Used properly, in fact, a Monte Carlo simulation can decrease rather than increase your financial uncertainty.
A Monte Carlo simulation is a computer program that juggles thousands of different variables to determine the performance of a portfolio over a period of time. It's a much more sophisticated way of retirement planning than, say, simply looking at historical rates of return. An historical analysis assumes that what happened in the past is likely to happen again in the future; if average returns were 8% over a given period in the past, then they are likely to be 8% in the future, too. A Monte Carlo simulation takes many other factors into account, including the variability of returns (high in some years and low or negative in others), fluctuating inflation, interest and unemployment rates, as well as bullish and bearish markets. The computer crunches all these numbers and more to project how your portfolio would perform under different scenarios. It then cranks out a percentage-the odds that your savings and investments will be enough to see you through retirement.
"A Monte Carlo allows you to stress test your portfolio before any of the events in the simulation actually happen," says Christopher Jones, chief investment officer with Financial Engines, a Web-based financial-planning service that uses the simulations. "You can see the peaks and troughs of possible events and get a real sense of the potential impact on your retirement income."
In short, Monte Carlo simulations allow you and your financial planner to better account for risk. If you're close to retirement, you obviously want the risk of missing your income goals to be very, very low. If you're further away, a higher risk might be acceptable, since you would have more time to make any necessary corrections. The calculation can show, for example, how conservative investments with low rates of return might leave you with a shortfall, or how more volatile stocks could expose you to big gains or losses. By charting a range of potential outcomes, the simulation can help you achieve the right balance between risk and return for your portfolio.
As an illustration, let's assume that you're 60 years old. You intend to retire at 65 and plan to live off the income from your savings and 401(k) investments. If the market behaves, you should be o.k. But a Monte Carlo simulation can tell you how some big and unexpected dive (maybe because of a terrorist attack or an oil shock) or a change in your financial priorities (maybe because you want to travel more or need to support a relative) could affect your income.
Let's say that under the best-case scenarios your chances of having enough money for retirement are 95%, a range you're pretty comfortable with. If your chances suddenly drop to 85% under the worst-case scenarios, though, you might want to do something about it. The simulation can tell you exactly how much more you'll need to feather the nest to get back into your comfort zone. "To get the probability of success back up," says Jones, "you could decide to save more, or to work an extra year or two, or to increase your risk by investing more, which could leave you even worse off. Or, you could decide to live on a bit less money." Of course, none of the worst-case scenarios might ever happen. The beauty of a Monte Carlo, though, is that it enables you to be ready if they ever do.
Dan Candura, CFP®, a member of CFP Board's Board of Governors and president of the Massachusetts investment advisory firm PennyTree Advisors, compares Monte Carlo simulations to predicting the paths of hurricanes. Weather forecasters can easily show where they think a hurricane will go. Close to the storm's present location, there is a pretty narrow band of possibilities. But further away in time, that band becomes much wider because the greater number of variables makes the path of the storm more unpredictable. "It's the same with investment portfolios," Candura says. "You have to pay attention to what's close, but you also have to keep an eye on what's further away to make sure your investments are on course, that the band of income possibilities remains within a comfortable range."
Candura cautions that Monte Carlo simulations need to be properly applied and interpreted if they're not to end up as what he calls "black box gobbledygook from someone wearing a fancy tie." If you're seeing an adviser who uses the technology, Candura suggests making sure that he or she is not just punching numbers and that as your priorities change, so do the simulations. "Monte Carlos are not cast in concrete but in oatmeal," he says. "You should be able to see the effects of moving or changing a goal. They're tools for driving decision-making, not ratifying decision-making."
Monte Carlo simulations are complex mathematical computations. But then again, Candura says, "People's lives are complex, too, sometimes so complex that they think things like their retirement are too difficult to plan. Doing a Monte Carlo simulation once a year or so enables you to plan, and to continually ask yourself: Is the plan going to work?" Which is sort of like predicting the path of a hurricane. You don't need a weatherman to know which way the wind blows, but a Monte Carlo can provide some shelter in case a storm heads your way.
ONLINE RESOURCE: There are a number of sample Monte Carlo simulations that you can try out on the Web. Should you decide to have a complete Monte Carlo simulation done, you should first talk to a financial professional. The Retirement Income Calculator on the Web site of T. Rowe Price, an investment management firm based in Baltimore, Maryland, employs the technology and is simple and straightforward to use.

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