The IRS is now accepting 2018 tax returns, and they're due on April 15, 2019. Popular tax programs often advertise "free" returns before hitting you with an upsell, but here's how you can do your taxes for free.

Incomes Below $66,000: IRS Free File

Here's a secret: If your income is $66,000 or below, you can use the IRS's Free File service. This is a partnership between the IRS and tax software companies like TurboTax, H&R Block, TaxAct, TaxSlayer, and others.

To use these free programs, you must head to the IRS's Free File Software Offers website and click through to the tool you want to use. You can't just go to the tax software's regular website, or you won't receive this offer. But, if you do click through here and qualify, you can use all the features you want with no attempted upsells---even in programs like TurboTax and H&R Block, which are notorious for charging you extra to use certain forms and "get your maximum refund."

To put it another way: The "Free File" versions of the tax software are different from the normal "free" versions on their websites. You have to know they exist and seek them out.

And yes, this does seem to be a secret. As MarketWatch points out, 100 million Americans are eligible to file their taxes for free, but only 3 million Americans do.

Read the fine print carefully before you get started. For example, if you need to file a state tax return, not all the programs will help you. TurboTax will only let you file a free federal return if your adjusted gross income (AGI) is $34,000 or less. H&R Block covers more people and will let you file for free if your income is $66,000 or less and your age is between 17 and 51.

We recommend you click the "Lookup Tool" button and fill in the details about your age, income, and state. The IRS website will tell you which tax-filing tools you can use for free and point you to ones that can also do your state taxes for you if your state requires you to file a tax return. If you need help finding a piece of software that can do your state taxes for free, the website of your state's revenue department may provide more information.

Anyone: Credit Karma Tax

If your adjusted gross income is $66,000 or more, you can still do your taxes online for free. You just have fewer choices.

Credit Karma offers free tax software. Really, it's completely free: There are no upsells because Credit Karma never charges for anything. Like with Credit Karma's credit score product, Credit Karma makes money through showing you offers based on your financial situation. And, unlike FreeTaxUSA, which offers free federal returns, Credit Karma also lets you file a state tax return for free.

While anyone can use Credit Karma to do both federal and state taxes with no income limit, Credit Karma does not support certain situations. For example, Credit Karma can't help you with part-year state returns, multiple-state returns, nonresident state returns, and the foreign tax credit. Consult the list and verify that Credit Karma supports your situation.

Beyond that, Credit Karma's tax software is a bit new. We've seen a few reports of problems online, so you may want to run your information through another tax program and double-check the numbers before filing---you can often do this for free with programs like TurboTax for which you pay only when you file. If Credit Karma's numbers match, they're probably solid, and you can file through CreditKarma without paying anything.

Incomes Above $66,000: Free Fillable Forms

If you can't or don't want to use CreditKarma, there's still another option. As the IRS points out, people whose income is about $66,000 can still do taxes online via free fillable forms.

Yes, we said fillable forms. It's kind of like doing your taxes on paper, but the forms do some basic calculations for you. If you're comfortable dealing with the IRS's paper income tax forms yourself, this is a free option. You can e-file from the forms website when you're done, so you don't even have to print out and mail anything. But there are some situations the forms don't support.

This service only includes federal tax forms. You're on your own for state taxes. If your state requires you to file a tax return, you may be able to find similar free fillable forms on your state's tax website.

Let's be realistic, though. If you have a pretty simple tax return, these forms should be pretty quick to fill out. And, due to changes in tax law, there's a good chance you'll be taking the standard deduction instead of itemizing your deductions---even if you itemized last year. That might make these simple to fill out.

Then again, if you have pretty simple taxes, you can always just use Credit Karma for a nicer interface.

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Of course, these are only the free options. You can always pay for another program. TurboTax often earns top marks in reviews of tax software, although it's a little on the pricey side.