Starting a side hustle. You may have started driving for Uber, delivering food for Postmates or taking on other freelance work as a way of bringing in extra cash. But the move can trigger a tax bill, tax experts say. For starters, you are probably not having taxes withheld from the paychecks you earn as an independent contractor, says Lisa Greene-Lewis, a certified public accountant and tax expert with TurboTax. That means you could be hit with a tax bill at the end of the year, she says.

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Some freelancers who still have a traditional 9-to-5 job may be able to avoid that tax hit by having more taxes withheld from their paychecks by their main employer, Greene-Lewis says. For other people, the surprise tax bill may be a hint that they may need to start making estimated tax payments every quarter to avoid falling behind on taxes, she adds.

Another thing to keep in mind is that freelance earnings of $400 or more are subject to self-employment taxes, meaning that you must pay both the employer and employee share of Social Security and Medicare taxes. That adds up to a total tax rate of 15.3 percent, says Cari Weston, a director with the American Institute of CPAs. However, self-employed workers can also deduct the employer portion of those payroll taxes, which account for half of the tax rate, or 7.65 percent, Weston says. They may also be able to write off some other business-related costs associated with their side gigs, such as advertising, marketing and software, that can help lower their tax bill, Greene-Lewis says.

Saying “I do.” Once the vows are exchanged and the honeymoon is over, married couples filing their first joint tax return could come across what’s known as the marriage penalty — or a higher tax bill than they would have owed if they each filed separately. This typically happens when the two spouses earn similar incomes. Getting married can land them in a higher tax bracket and therefore result in a bigger tax bill, Weston says.

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For example, a couple with each spouse earning $100,000 a year would pay nearly $800 more in income taxes after getting married than if each person had filed separately as a single person, according to a calculator from the Tax Policy Center. Depending on how much each spouse is withholding from his or her paycheck, the difference could result in a tax bill. (However, some couples may end up with a lower tax bill, or what’s known as a marriage bonus. If one person is not working or earns significantly less than the other spouse, it could put them into a lower tax bracket.)

Filing for divorce. If you got divorced, then you probably won’t qualify for some of the tax deductions you claimed as a married person. For example, divorced couples with children will find that only one parent can claim child-related tax breaks, such as the adoption credit, the earned-income tax credit and education credits, says Dave Du Val, chief customer advocacy officer at TaxAudit.com. For some people, becoming single could also mean landing in a higher tax bracket, Greene-Lewis says, especially if their spouse earned significantly less money — and brought them into a lower tax bracket.

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Tapping into your retirement account. If you withdrew money from, say a 401(k) or an individual retirement account, then you might owe Uncle Sam. People who withdraw money before age 59½ must also typically pay an early-withdrawal penalty tax of 10 percent unless they qualify for an exception because of a medical emergency, purchase of a first home or another financial hardship.

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Financial firms will usually automatically withhold 20 percent before paying out such early-retirement distributions, but it may not be enough to cover all of the taxes and penalties owed, Du Val says. For some people, the withdrawal may push them into a higher tax bracket, which could increase their overall tax bill, Greene-Lewis says.

Selling your home. You may owe Uncle Sam if you sell a home for much more than what you bought it for. If you’re single and made a profit of more than $250,000 on your home, or if you’re married and had gains greater than $500,000, then you may owe taxes on the sale. Also, any gains from the sale of a vacation home or rental property generally needs to be reported as capital gains, which would make it subject to a 20 percent tax if the home has been owned for longer than a year.

Losing your job. Some people may not realize that income received from unemployment benefits is taxable, Greene-Lewis says. While recipients are given the option of having taxes withheld from their unemployment checks, some people may overlook that or decline if they are in a tight financial situation, she says. However, taxes on those benefits will be due when they file their tax returns and could eat into any tax refund they are expecting.

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Receiving an inheritance. If someone dies and leaves you an asset that they would have owed taxes on, that asset is now taxable to you, Du Val says. For example, say you inherit a relative’s retirement savings. If the person would have owed taxes on the savings, you would owe income taxes on that inheritance, he says. Many common forms of inheritance, however, including life-insurance payouts and cash transfers, do not trigger tax bills for the recipient, because there was no tax bill owed by the person who died, Du Val says. Some very large inheritances that are greater than $5.49 million per individual may be subject to the estate tax of up to 40 percent.

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People inheriting property could also face tax bills depending on what they do with it. Take the example of a person who inherits a house and sells it right away. He may not owe any taxes if the sale price is the same as the inherited price, Weston says. But someone who inherits a house and sells it years later at a higher price would owe taxes on the difference, he says.

Winning a vacation, car or other prize. You probably already know to expect a huge tax bill if you strike it rich by winning the lottery. But winning noncash prizes such as a car, or a vacation, can also trigger a tax bill, Weston says. Winners will typically owe income taxes on the cash value of that prize and should report it on their tax returns. Some game shows will make that reporting easy by sending participants a 1099 form, Weston says.

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But some people may also face tax bills after coming across less obvious prizes, such as fans who catch a home-run ball at an important baseball game. That ball has value and is taxable, Du Val says. If you returned the ball in exchange for tickets or a memorabilia such as a signed jersey, that may also be considered taxable income, but tax experts say the rules are not clear.