Review our breaks as a slide show.

No doubt about it: The opportunity to make mistakes is almost unlimited, and missed deductions can be the most costly. About 46 million of us itemize on our 1040s — claiming nearly $1 trillion worth of deductions. That’s right: $1,000,000,000,000, a number rarely spoken out loud until Congress started debating economic-stimulus plans to combat the Great Recession.

Another 85 million taxpayers claim more than a half-trillion dollars’ worth using standard deductions—and some of you who take the easy way out probably shortchange yourselves. (If you turned 65 in 2009, remember that you now deserve a bigger standard deduction than the younger folks.)

Yes, friends, tax time is a dangerous time. It’s all too easy to miss a trick and pay too much. Years ago, the fellow who ran the IRS at the time told Kiplinger’s Personal Finance magazine that he figured millions of taxpayers overpaid their taxes every year by overlooking just one of the money-savers listed below:

1. State sales taxes. Although all taxpayers have a shot at this write-off, it makes sense primarily for those who live in states that do not impose an income tax. You must choose between deducting state and local income taxes or state and local sales taxes. For most citizens of income-tax states, the income tax is a bigger burden than the sales tax, so the income-tax deduction is a better deal.

The IRS has tables that show how much residents of various states can deduct. But the tables aren’t the last word. If you purchased a vehicle, boat or airplane, you get to add the state sales tax you paid to the amount shown in the IRS tables for your state, to the extent that the sales-tax rate you paid doesn’t exceed the state’s general sales-tax rate. (Download IRS tables in .pdf format here).

The same goes for any homebuilding materials you purchased. These items are easy to overlook, but they could make the sales-tax deduction a better deal even if you live in a state with an income tax. The IRS even has a calculator on its Web site to help you figure the deduction, which varies depending on the state where you live and your income level.

2. Reinvested dividends. This isn’t really a deduction, but it is a subtraction that can save you a bundle. And this is the break that former IRS commissioner Fred Goldberg told Kiplinger’s a lot of taxpayers miss.

If, like most investors, your mutual fund dividends are automatically used to buy extra shares, remember that each reinvestment increases your tax basis in the fund. That, in turn, reduces the taxable capital gain (or increases the tax-saving loss) when you redeem shares. Forgetting to include the reinvested dividends in your basis results in double taxation of the dividends — once when you receive them and later when they’re included in the proceeds of the sale. Don’t make that costly mistake. If you’re not sure what your basis is, ask the fund for help.

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