Taxpayers who are deployed internationally as a result of active military service may be granted an extension to file. The Department of Defense maintains a database of all actively deployed service members, which it shares with the IRS, so this excuse is pretty easy to verify.

Individuals who were not able to access their tax files due to incarceration or who were incarcerated late in the filing season, causing them to miss the filing deadline, are also often granted leniency.

Leniency is only granted in the case of severe illness. Any more run-of-the-mill health problems or feelings of stress by either the taxpayer or their preparer aren’t valid excuses for late filing.

In addition, regardless of how much work they've taken on, overwork on the part of the taxpayer or preparer is not a valid excuse either.

If a taxpayer files late because they were misled by an IRS employee, and he can prove it, then penalties won’t be assessed. Predictably, proving this can be easier said than done, particularly in the case of non-documented conversations. The more likely case where this excuse may arise is if an official IRS publication provides inaccurate information that is then relied on by the taxpayer or preparer.

If a taxpayer can prove he had a valid medical reason (and offer documentation to prove it) for not filing on time, the IRS will generally waive any penalties. This leniency may extend to the serious illness of a close family member as well, but the bar appears significantly higher when the taxpayer her- or himself isn’t afflicted.

Additionally, under certain circumstances, the IRS has allowed extensions for returns that weren’t timely filed due to the death of a spouse or other close relative.

Paying taxes isn’t voluntary. Regardless of your beliefs, the government expects their share, so you have to file returns. Over the years, many have tried to spread myths about taxes not being mandatory for one nebulous reason or another, but the service has no patience for either the rumor-spreaders or those who believe them. In fact, the IRS finds these rumors so destructive (and infuriating) that they’ve been known to levy immediate fines against anyone who attempts to cite religion or philosophy as the reason for voluntarily not filing (in addition to the usual penalties).  

For all the jokes we can make at the IRS’ expense, they do realize how complicated this all is and aren’t looking to come down too hard on well-meaning folks who honestly mess up. That’s why they offer a First Time Abatement Waiver, which basically says that as long as this is your first offense, your documents are filed correctly and you don’t owe any money, then you’re off the hook. The first honest mistake is a freebie.

In the past, the IRS has not come down on those who can prove that they didn’t file on time because their tax files were lost or destroyed. Circumstances ranging from having the files stolen by a burglar to the taxpayer’s house burning down, taking the files with it, all fall under this exception. Importantly, however, the destruction or loss must be accidental. The IRS will look closely into these claims, as a fair few unscrupulous individuals have staged the destruction of their own documents.

“I forgot” is an excuse that the IRS will not look on kindly (and yet still hears all the time). It doesn’t matter if you can prove that the documents were timely completed and simply never filed due to an oversight on the taxpayer’s part. The IRS holds the taxpayer responsible for keeping track of all filing deadlines. The IRS doesn’t care when the forms were prepared (in terms of late filing at least); they care when they receive the documents.

Believe it or not, acting on bad advice, even if it comes from a professional, doesn’t necessarily free a taxpayer from penalties for late filing.

It’s unsurprising that advice from a non-professional wouldn’t hold any weight with the IRS. They don’t care what the mechanic told you to do, after all, even if he is your brother.

But, when it comes to professionals, the question becomes whether the person who offered the advice is licensed and competent, and if the advice the taxpayer relied on was "reasonable." 

As with just about every other law on the books, ignorance isn’t a valid reason for not complying. The IRS assumes that taxpayers will take responsibility for meeting their obligations in a timely and lawful manner, or hire someone to do the same.