Their shared flaw? "Garbage In, Garbage Out" ("GIGO").
70 percent of current income is the model widely used for calculating the amount of income you will need when you retire. Unfortunately, that model, like Catastrophe Models, is not based on experience but on opinion.
In a newly released study, Professors John Karl Scholz and Ananth Seshadri wrote about "What Replace Rates Should Households Use?" Their study was published by the University of Michigan Retirement Research Center. Here is a pdf copy posted online of their Research Paper. They found many reasons why 70 percent of currrent income is a flawed model for calculating retirement income, but the biggest is the simplest: Calculate your retirement needs based upon your experience, not opinions.
Even if the opinions are your own, but even more so if the opinions are someone else's.
Here is a web page with some of the research papers made available online of Professor John Karl Scholz, Economics Professor of the University of Wisconsin-Madison. Here is the web page listing publications of Economics Professor Ananth Seshdari, also at the University of Wisconsin-Madison.
Oh, and forget about using those online calculators unless you are actually trying to fail. "In other words, if you're using an online calculator to plan your retirement, you might be undersaving or oversaving by a wide margin." MarketWatch, "Typical Retirement Savings Rate Models Are Often Flawed, Professors Say," published online in St. Petersburg Times Online, Friday, November 6, 2009.
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