Getting married isn't just a huge commitment -- it's a major financial event in your life. To avoid making costly mistakes, you have to know the tax provisions that affect newlyweds.

In the following video, Dan Caplinger, The Motley Fool's director of investment planning, runs through three of the key must-know facts newlyweds should know. Dan points out that your marital status as of Dec. 31 is what the IRS looks at for filing purposes, so if even if you got married on the last day of the year, you're treated as married for the whole year. Dan then notes that different brackets apply to married taxpayers compared to singles, with some couples enjoying a marriage bonus while others suffer a marriage penalty. To make sure you have the right amount withheld from your paycheck as a married couple, Dan advises going to your HR department to complete a new Form W-4 to adjust your tax withholding. 

Dan Caplinger and The Motley Fool have no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.