Tax day has already come and gone. But what if you still haven’t filed or paid?

It’s only a few days late at this point thanks to some delays in the federal tax deadline this year. Or maybe it has been a few years. Regardless of how behind you are, it’s time to address it. This isn’t a problem that will go away on its own and it’s only going to get worse the longer you ignore it.

It’s true, not everyone has to file federal income taxes, but most adults do.

People whose income falls above a certain threshold for their age and filing status are required by law to file. In general, those who are not required to file are lower income. If you are unsure whether you meet the threshold, check the IRS website.

Not filing a federal return means you may face a “failure to file” penalty. It is normally 5 percent of the unpaid taxes for each month that a filing is late. It won’t exceed 25 percent of your unpaid taxes. If you owe money and have not paid on time, you also face a “failure to pay” penalty. This is 0.5 percent of your unpaid taxes and may be up to 25 percent of your unpaid taxes, too.

In general, the IRS is willing to work with you if you are behind. If you can show reasonable cause for not filing or paying on time, you will not have to pay a late-filing penalty or late-payment penalty. But, in extreme cases, if the IRS believes you are evading taxes, it can seek criminal charges.

If you aren’t able to pay now but can soon, the IRS offers up to 120 days to pay in full, according to the Taxpayer Advocate Service, an independent part of the IRS dedicated to helping taxpayers. It’s not a formal payment option, so there’s no application or fee, but interest and any penalties will continue to accrue until it’s paid off.

You can also apply for an installment agreement, which sets up a fixed monthly payment. Or you can request an “Offer in Compromise” that allows you to pay less than the full amount you owe, although experts say these are not widely granted.

Here’s a bit of good news: if you haven’t filed in the past you may actually get some money back. The IRS reports they had about $1 billion in unclaimed refunds last year, so don’t leave that money on the table, said Lisa Greene-Lewis of Turbo Tax.

If you have a refund due, there is no penalty for failing to file your tax return by the deadline. But you only have three years to file and claim, or you’ll forfeit your refund.

It’s typically students, part-time workers and others with low to moderate income who overlook filing and are due a refund. They may not even meet the threshold that requires them to file. But to collect the money they are owed, they must file a tax return.