Tax Day is tomorrow. Here’s what you need to know to file your return.

The Internal Revenue Service building in Washington, D.C., on Jan. 19.STEFANI REYNOLDS/AFP via Getty Images

Massachusetts taxpayers have until Tuesday, April 19, to file their federal and state returns this year.

But this has been a frustrating year — the IRS warned taxpayers and lawmakers on the tax season’s first day in January. Staffing shortages and a backlog of some 10 million unprocessed returns from last year were expected to bog down the system.

And if the past is prologue, don’t expect to get an IRS staffer on the phone if you have a question. According to a report during last year’s tax season in the Washington Post that quoted the national taxpayer advocate within the IRS, only about 1 out of every 50 calls got through to an IRS customer service representative on the agency’s toll-free line (800-829-1040).

In January, Senator Elizabeth Warren and 12 other members of the Senate Democratic caucus wrote to Treasury Secretary Janet Yellen arguing that at a minimum the IRS needs a 14 percent increase in annual funding and an $80 billion investment over a decade.

And they decried a “decade-long gutting of the IRS budget, which has prevented the agency both from taking action against wealthy tax cheats and providing adequate assistance to the majority of Americans trying to honestly file their taxes.”

With all of that in mind, here are some answers to questions you may have as you file your 2021 taxes.

We include basics about who must file, how to file, where to get help, plus some important information for anyone who collected unemployment benefits in 2021 or received the expanded child tax credit or a stimulus check.

Q. When is the tax-filing deadline this year?

A. The deadline for filing both federal and state tax returns in Massachusetts (and Maine) is April 19, a day later than the deadline in other states because Massachusetts and Maine celebrate the Patriots Day holiday on April 18.

The deadlines in 2021 (May 17) and 2020 (July 1) were pushed back due to the pandemic. It’s possible the IRS will extend the deadline again this year, but don’t count on it.

Q. What’s the deal with unemployment benefits?

A. Unemployment benefits are considered taxable income by both the federal and state governments, with some exceptions for people who have low income. And it doesn’t matter if the benefit was funded by the federal or state government. (Unemployment benefits, however, are not subject to Social Security or Medicare taxes.) The state Department of Unemployment Assistance, which administers the benefits, provides an option for withholding taxes from weekly benefits. If you did not opt for withholding, you now may be liable for a sizable lump sum in owed taxes.

The DUA says on its website that form 1099-G, which tallies total benefits for 2021, is available by checking your DUA account.

Q. But what if the state is trying to take back some of the benefits I received?

A. How much you received in unemployment may be subject to change because, as the Globe has reported, the DUA made as much as $2.7 billion in overpayments to about 383,000 claimants during the pandemic, through no fault of the claimants. The state is now seeking reimbursement of at least some of that. Obviously, if you paid taxes on unemployment benefits, and you later pay those benefits back to the state, you should get a refund on the taxes you paid. The DUA says the 1099-G form it issues will be revised to reflect any paybacks.

Q. What’s the deal with the expanded child tax credit?

A. Families that received the child tax credit in 2021 will have a little extra accounting to do this year. That’s because of changes made last year in the longstanding program. For years, the child tax credit benefited families once a year in the form of lower taxes and often a substantial tax refund in the spring. A tax credit reduces your taxes dollar-for-dollar, as opposed to a tax deduction, which reduces the amount of your income that is considered taxable and is far less lucrative. A family that owes $5,000 in taxes but has a $3,000 tax credit pays only $2,000 in taxes. It works like a cash grant.

Q. So, what has changed?

A. In March, the Biden administration and Congress expanded the child tax credit as part of the $1.9 trillion pandemic relief bill. One key change was to send families hundreds of dollars in cash monthly, rather than making them wait for the lump sum at tax time.

Q. How does that affect tax filers?

A. Monthly cash payments were made last year for six months (July through December) after passage of the pandemic relief bill. So, in 2021, families got their child tax credits in two forms: the traditional, wait-for-your-refund sort in January through June, and the new, cash-in-your-pocket sort for the rest of the year.

To properly account for the whole year, the IRS needs to know how much money families received in monthly cash payments. Families may add up how much they received by checking their bank or other records. But to rely on your records is to risk a mistake, even a minuscule one, that could trigger a long delay in a refund.

Q. So what is the IRS asking tax filers to do?

A. The IRS recommends that you keep an eye out in the mail for a tax document known as a letter 6419, which contains the amount you received in cash. Use it in the hopes of a speedy refund.

More information is at this site: https://www.childtaxcredit.gov/.

(Cash payments to families with children were discontinued this month because Congress did not extend the program, which was generally opposed by Republicans.)

Q. Are my stimulus checks taxable?

A. No. Technically, the money you received in a stimulus check isn’t income (which is almost always taxable). The money the federal government paid to you is actually a tax credit, known as a recovery rebate credit. It’s a reduction in your federal income taxes that works like cash, paid well in advance of the due date for taxes.

The 2021 stimulus checks were disbursed to eligible recipients starting in March of last year, worth up to $1,400 per qualifying taxpayer and each of their dependents. Even though stimulus checks are not taxable, they need to be reported on 2021 tax returns.

Q. Overall, how does it look for a quick federal refund?

A. The IRS says, if you file electronically, have direct deposit, and make no mistakes in the information you include in your return, you should get your refund within 21 days. Once you file, you can check the status of your pending refund by checking the IRS’s Where’s My Refund site or by using its IRS2GO mobile app.

To get your update online, you will need your Social Security number and the exact amount of your refund for authentication.

Q. Who must file a federal tax return?

A. Anyone who received income over a certain amount in 2021, including US citizens (residing in the United States or abroad) and lawful permanent residents (green card holders). If you earned more than $12,550 ― $25,100 for a married couple filing jointly ― you are required to submit a federal tax return. Those are the standard deduction amounts.

Q. What about state taxes?

A. Anyone who had a gross income of more than $8,000 in Massachusetts must file a state tax return. If you want to claim certain refundable credits, like the Earned Income Tax Credit or Circuit Breaker Credit, you must file a tax return.

The state exempts Social Security benefits and income from public pension funds from its income tax.

Q. Can I file a paper tax return?

A. Technically, yes. Both the IRS and the state permit paper filings, but the IRS really doesn’t want you to do that, warning it will cause delays. Fewer than 10 percent of federal taxpayers now file by paper.

Q. Do I have to pay to file electronically?

A. For those with an adjusted gross income of $73,000 or less, no. The IRS provides free online tax preparation and filing options in partnership with online tax preparation companies. For more information, go to this site: https://www.irs.gov/filing/free-file-do-your-federal-taxes-for-free.

Q. Are there other options for getting no-cost assistance with filing taxes?

A. Here are two longstanding programs that offer free basic tax return preparation to qualified individuals: Volunteer Income Tax Assistance (VITA) and Tax Counseling for the Elderly (TCE). In general, they assist people who make $57,000 or less; people with disabilities; and limited English-speaking taxpayers. Go to this site: https://irs.treasury.gov/freetaxprep/.