When I entered my mutual fund 1099-DIV, my tax bill increased by about $1000. Why? This has never happened to this extent before? How can I prevent this in the future?

[Rachel_W · Accepted solution]

It sounds like your Mutual Funds had a lot of Capital Gains Distributions (Box 2a of Form 1099-DIV) at the end of 2017. This often happens when the stock market has a booming year because Mutual Funds are required to pay out substantially all of their gains by the end of the year. 

Even though Capital Gains Distributions receive preferential tax treatment, they can still increase your tax liability by a significant amount when the payouts are large. 

There is not really much you can do to avoid this other than have a good cushion of taxes withheld during the year.  Most Mutual Funds report what they are going to pay out quarterly or annually so you can check their website to keep an eye out for any big distributions. If the distributions look to be much larger than you normally receive, you could choose to pay in estimated taxes to avoid owing when you file your return.