The Internal Revenue Service has a calculator (go to www.irs.gov and search for "withholding calculator") that can help you figure out if you need to adjust your withholding.
"They searchout somebody who has similar characteristics to their own, so youcan imagine this theory being played out to extremes with plastic surgery, " said Dr Papadopoulos.
But some aspects of the service need work: The selection is spotty (in Boston, at least, you can't get a Pepsi or a Hershey bar), and the search engine can be a hassle to figure out.