And even if a mistake -- either on your computer or paper forms -- doesn't cost you cash, it could delay the receipt of any refund you're expecting.
Now that you're facing the final Oct. 15 deadline for your tax-filing extension, make sure you don't make any of these filing mistakes.
1. Pay your Roth conversion taxes
A lot of taxpayers have taken advantage of the tax law change that now allows anyone, regardless of income, to convert a traditional individual retirement account to a Roth IRA. But if you made such a change in 2010 when this conversion was first allowed, you have a tax task to take care of on your 2012 return. A special provision allowed individuals who moved their money into a Roth IRA in 2010 to spread the taxes due on converted amounts equally over the 2011 and 2012 tax years. The first half of those conversion taxes was due with your 2011 tax return. Make sure you pay the rest of the taxes with your 2012 return.
2. Homebuyer tax credit complications
Since its creation, the first-time homebuyer credit went through significant changes. It started as a $7,500 interest-free loan from Uncle Sam, changed into a true tax credit of up to $8,000 for a first-time buyer and added a $6,500 tax credit for a previous homeowner moving up to another house.
All the revisions to eligible buyer guidelines, purchase time frames, income thresholds, home price restrictions and payback requirements are a tax-filing minefield. If you're not careful, a mistake here could end up costing you the credit or at least slowing down the processing of your return.