If you're getting a huge enough refund to consider a down payment on a sports car, you really need to sit down for 10-15 minutes and decrease your withholding.
^ I'm with stupid ^
I don't like giving the government interest free loans...
Meh, while this is fundamentally true, it really doesnt add up to much assuming your a typical American saver. Lets say you get a fairly large return of $8,000. Lets say you adjusted your withholding and invested those excess funds throughout the year in a money market savings account transferring the excess of $333 ($8,000 / 24 per periods in a year) immediately via direct deposit. Assume your money market account pays interest at an annual rate of 1.5%. For simplicity sake multiply $4,000 * 1.5% = $60 in interest income for the entire year (I used $4K instead of $8K because your not depositing the $8K on January 1st and this assumes a average annual balance). If your in the 25% tax bracket your only netting $45. Not much of a benefit.
Now there are other options you have like increasing your 401k contribution and then adjusting your withholding so that you have roughly the same take home pay per paycheck. Or you could roll the dice in the market with those excess funds as well.
My point is for some who only maintain a money market savings account, it actually probably benefits them to receive a large chunk of money in the Spring rather than an extra $333 per pay period which they will likely spend on other worthless crap like Ipads

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