• April 18 is the last chance for most Americans to skip late filing and payment penalties for 2021 federal taxes.
• You can still submit an extension on April 18 to avoid a monthly fee for missing the tax due date.
• However, you'll need to make an estimated payment to bypass late fees on taxes owed.

It's finally here: April 18 is the 2021 federal tax filing deadline for most Americans.

As of April 8, the IRS had received more than 103 million returns and sent 70 million refunds, totaling over $222 billion. But that still leaves millions to be filed with limited time remaining. 

Doug Campbell, a CPA and vice president of tax support at Liberty Tax, said there's been a "pretty big spike in returns" that started over the past couple of weeks.

"Maybe they filed in May or June over the past year or two, and all of a sudden, they realized they don't have that extra time," he said.

Certain disaster victims, taxpayers serving in combat zones and those living abroad may automatically have more time to file, according to the IRS.

However, if you don't qualify for more time and are not ready, there's still time to file an extension, bumping your due date by six months to Oct. 17, Campbell explained. 

You can file an extension by sending Form 4868 electronically with IRS Free File, regardless of income, or by making a payment through IRS Direct Pay and choosing "extension" as the reason.   

Sending an extension by April 18 may avoid a late filing penalty of 5% of your unpaid balance per month, capped at 25%. But it won't bypass a monthly late payment fee of 0.5%, limited to 25% of taxes owed.

"Just understand you still are going to have to come up with as accurate as possible an estimate of how much tax you may owe," Campbell said.

If you can't cover your estimated balance, you may qualify for a payment plan through the IRS. But you must file an extension or return to be eligible. 

What to know before filing

If you're planning to file your return, you can save money with IRS free file if your adjusted gross income is $73,000 or less for 2021, which is roughly 70% of taxpayers. And you can use Free Fillable Forms, if your AGI exceeds $73,000.

You're likely to receive your refund within 21 days by filing an accurate, electronic return with direct deposit. But mistakes may send your return into what the IRS calls "error resolution," requiring manual review, Campbell warned.

Your return should mirror any tax forms the IRS receives, such as your W-2, investment income and more. You'll also want to double-check IRS letters for details on stimulus checks and advance child tax credit payments.  

"We urge extra attention to those who received an economic impact payment or an advance child tax credit last year," IRS Commissioner Chuck Rettig said in a statement. "People should make sure they report the correct amount on their tax return to avoid delays."

The IRS mailed roughly 7.4 million "math error" notices for stimulus payment mistakes from Jan. 1 through July 15, 2021, halting refunds, and many are still waiting for a resolution.

"Mistakes are much easier to come by if you're scrambling at the end of the game instead of having everything in line ready to go," Campbell added.