By calculating your tax refund ahead of time, you can make sure that you don't overestimate your refund and thus spend (or plan to spend) money that you don't really have. On the flip side, if the calculators determine you should be getting a healthier refund than you imagined, maybe you can start making some fun plans to use your refund money. I know that if I don't plan ahead, I end up using my refund to pay for car insurance or some other boring expense, when it would be much more enjoyable to use it for a vacation!
Both H&R Block and Turbo Tax have easy to use and very popular refund calculators, but rather than take my word for it, check out the links to these and other useful tax-related resources on the File My Taxes Online website, a website that serves as an information portal and doesn't try to sell you any tax prep services, etc. They simply give the latest news and links about taxes, tax law, tax-related tools, and more.