Many mistakes are harmless -- such as when you forget to run the dishwasher overnight. Other mistakes, though, can be quite costly. Many tax blunders fall into that latter category, as they can cost you hundreds, if not thousands, of dollars.

Here, then, are 10 tax mistakes to avoid making, in order to keep more of your hard-earned dollars in your own pocket instead of in Uncle Sam's.

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1. Failing to keep track of your spending and receipts

It's easy to ignore our spending until tax season, when we suddenly need to know how much we spent on child care or medical expenses, or what we gave to charity. Don't wait until April to start digging through folders and stacks of papers for whatever receipts you can find. Make your life easier by maintaining a "taxes" folder or shoebox, into which you drop any receipts or other documents that will support your tax return -- throughout the year. For example, keep receipts from your charitable giving and medical spending to support possible deductions. Track your spending, too. If you find that you're spending a lot on healthcare, that might mean you'll be able to itemize your deductions.

2. Not contributing to retirement accounts

Another tax blunder is not making use of tax-advantaged retirement savings accounts. There are two main kinds of IRAs and 401(k)s -- the Roth and the traditional -- that offer two different kinds of tax breaks. The traditional IRA or 401(k) shrinks your current taxable income and gives you an up-front tax break, while the Roth IRA or 401(k) offers tax-free withdrawals in retirement. For 2018, the contribution limit for both kinds of IRAs is $5,500 for most people and $6,500 for those 50 and older. Meanwhile, a 401(k) has a much more generous contribution limit. In 2018, the limit is $18,500, plus an extra $6,000 for those 50 or older.

The table below shows what you might accumulate over various periods if you sock funds away aggressively and your investments average 8% annual growth:

Growing at 8% for:

$10,000 invested annually

$15,000 invested annually

$20,000 invested annually

5 years

$63,359

$95,039

$126,719

10 years

$156,455

$234,682

$312,910

15 years

$293,243

$439,864

$586,486

20 years

$494,229

$741,344

$988,458

25 years

$789,544

$1.2 million

$1.6 million

30 years

$1.2 million

$1.8 million

$2.4 million

Data source: Calculations by author.

If you contribute $10,000 to a traditional 401(k) and you're in a 25% tax bracket, you'll avoid paying $2,500 in up-front taxes. If you accumulate $400,000 in a Roth IRA over many years, you may withdraw it without paying taxes on any of it. Not making use of these accounts can result in a lot of unnecessary taxes paid.

3. Doing things that can increase your odds of being audited

While few people want to be audited, many people do things that can increase their chances of being audited. Here are the kinds of mistakes to avoid.

Failing to file a return -- or reporting no income: If you fail to file a tax return for any reason, the IRS may contact and question you. Even those with no income or no taxes due need to file a return, explaining that they have no income and/or demonstrating that they have no taxes due. Your odds of being audited are higher if you report no income -- even if you've filed a return.

Being messy or making mistakes: If the IRS's computers or workers can't tell, say, whether you've written a 6 or a 0, your return may be flagged for a closer look. If the IRS's math differs from yours, that can also trigger an audit. Double-check your math and be sure you're entering correct numbers in the correct boxes. One way to improve the accuracy of your return is to use tax-preparation software, instead of preparing your return by hand, and to electronically file your return. Remember to sign your return, too -- as unsigned returns can also draw the attention of the IRS.

Leaving out any required information, such as data from the 1099 forms your brokerage and other financial institutions have sent you: Failing to report any income or omitting any other information can raise flags at the IRS and get you audited. It might just be a seemingly inconsequential dividend payment that you didn't want to bother mentioning, but it needs to be included -- not only because it's the right thing to do, but also because the IRS will probably already know about that payment to you and will be wondering why you haven't mentioned it. Entities that pay you generally report having done so to the IRS -- whether they're reporting salary payments, dividend income, interest paid, or something else. The IRS then expects your return to include all of these payments.

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4. Not using your losses to offset gains

It's never a pleasure paying taxes on your capital gains, but if you're sitting on some paper losses (perhaps from stocks that have tanked that you haven't sold yet), you can use them to shrink your taxable gains -- potentially to zero. For example, if you have $6,000 in gains and you sell enough holdings to generate a loss of $4,000, you can pay taxes on only $2,000 in gains. If you have way more losses than gains, you can wipe out your gains entirely, then shrink your taxable income with up to $3,000 of your losses, and then carry over any leftover losses into the next year. (If you plan to buy back any of the losers you sold, be sure to wait at least 31 days, or you'll end up with a "wash sale" and won't be able to claim the capital loss on your tax return.) This strategy is best applied throughout the year, not just at tax time. A particularly good time to sell a certain holding for a gain or loss may be in August, not right at the end of the year.

5. Not paying attention to your holding periods

Don't sell any stocks without giving some thought to how long you've held them. At the moment, most of us face long-term capital gains tax rates (for qualifying assets that were held at least a year and a day) of 15%. Short-term capital gains are taxed at your ordinary income tax rate, which could be close to twice as high. So if you've held a stock you want to sell for 11 months, consider hanging on for another month and a day. Don't base any selling decision solely on taxes, but do include taxes in your thinking.

6. Not taking tax credits available to you

Tax credits often get less attention than tax deductions, which is a shame -- since they're far more powerful. While a $1,000 deduction can save you $250 if you're in a 25% tax bracket, a $1,000 tax credit can reduce your tax bill by a full $1,000.

Tax credits exist for all kinds of things, such as education expenses, energy-efficient home improvements, the adoption of children, the care of children and dependents, and much more. A particularly valuable credit, if your income is low enough to qualify, is the Earned Income Tax Credit, which might shrink your income by more than $6,000. The Child and Dependent Care Credit offers a credit of up to $3,000 for the care of one eligible dependent and up to $6,000, total, for two or more. And the Child Tax Credit offers $2,000 for every qualifying child you have who is under the age of 17 (as of the end of the tax year) -- subject to some rules and restrictions again, of course.

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7. Not using a health savings account (HSA) or a flexible spending account (FSA)

If you have a qualifying high-deductible health insurance plan, you can fund an HSA with pre-tax money, lowering your tax bill. That money can be used tax-free for qualifying healthcare expenses and it can accumulate over years, too, invested and growing. Once you turn 65, you can withdraw money from an HSA for any purpose, paying ordinary income tax rates on withdrawals -- and making the account serve as an additional retirement savings account. HSA contribution limits for 2018 are $3,450 for individuals and $6,900 for families. Those 55 or older can chip in an additional $1,000.

Flexible Spending Accounts are another option. They accept pre-tax dollars and let you spend them tax-free on healthcare expenses. They're not quite as wonderful as HSAs, though, as you need to use most of your contribution each year, or you lose it. Still, if you plan well, this can save you a lot in taxes. If you're expecting to pay $2,000 on braces for your child this year, sock that much into your FSA and you'll avoid paying taxes on it. Contribution limits for health FSAs are $2,650 for 2018.

8. Not taking your required minimum distribution (RMD)

This mistake can be very costly. Some retirement accounts, such as traditional IRAs and 401(k)s, require RMDs, expecting you to withdraw certain amounts each year. The deadline to take your distribution each year is Dec. 30, except for the year in which you turn 70 1/2. For that year, you have until April 1 of the following year to take your RMD. (It can be better to take it before the end of December regardless, though, lest you end up taxed on two distributions in one year.) Many people like setting up their account so that their RMD is sent to them automatically each year.

If you're in your 70s or beyond -- or if you're approaching 70 -- be sure to take your RMDs on time; otherwise, you can face costly penalties. The penalty is a whopping 50% of the amount you didn't withdraw on time, so if you were supposed to withdraw $8,000, you're looking at forfeiting $4,000! (Note that the IRS does let you appeal for a waiver.)

9. Not keeping up with changes to the tax laws

Our country's tax laws are not only voluminous and confusing -- they also change frequently. If you don't keep up with changes to tax laws, you may miss deductions or credits available to you -- or you might not be aware when some of them are no longer available. For example, a bunch of tax deductions are ending in 2018, such as many for job-related expenses. Be sure you're not making any tax decisions or plans based on false assumptions.

10. Not hiring a tax pro

Finally, for many of us, it's a costly mistake to not hire a tax pro to prepare our return. Sure, it will cost something -- but the benefit can well outweigh that cost. After all, most of us don't know the tax code inside and out, and only think about taxes for a few weeks of the year, at most. A savvy tax pro keeps up with changes to the tax code, is good at strategizing and finding ways to shrink tax bills, and is immersed in the tax world all year long. Don't just hire anyone, either. Ask around for recommendations. Consider hiring an "Enrolled Agent," a tax pro licensed by the IRS who is authorized to represent you before the IRS if need be. You might find one through the National Association of Enrolled Agents website.

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