Mistakes When Filing US Taxes: Filing Too Late, Inaccurate Information and Math Errors
- Del Sol CPA
- Feb 9
- 5 min read
Updated: Mar 25
Filing a tax return can be an intimidating and time-consuming process for even the most experienced taxpayers, and it certainly doesn’t help that making mistakes on your tax return can be costly, whether as a result of incurred penalties, interest on late payments, or simply leaving money on the table due to an oversight.
Our goal with this guide is to help you prepare for and be aware of some of the most common tax filing mistakes made by US taxpayers, and prevent you from having to pay unnecessary taxes or making mistakes that could result in significant fines or penalties. We’ll also tell you what to do when mistakes DO happen, so that you can relax a little and be equipped with the knowledge you need to face your taxes with confidence.
Bear in mind that we can’t cover every possible mistake that can be made on an IRS tax return, so we’ve selected the most common (and the most impactful) mistakes that are easiest to avoid, or could cost you the most.
Key points covered In this article:
The basics
The details
Claiming improper deductions
Misreporting or Underreporting income
Special considerations for overseas taxpayers
The Basics
Let’s start with some of the most basic (and common) mistakes made by US taxpayers every year. Following these basic guidelines will ensure that you avoid some of the most common and easily avoidable pitfalls when it comes to filing your US Taxes.
Filing Too Late
One of the most obvious (yet not uncommon) mistakes made by taxpayers is that of filing your taxes too late. The regular tax filing deadline for US taxpayers is April 15. You can extend this deadline by 6 months (to October 15) by filing an extension using IRS Form 4868.
US taxpayers living outside the United States are entitled to an automatic two-month extension.
Failing to file by the deadline will result in a fine based on the amount of your unpaid taxes! The details of calculating the penalty can be found on the IRS website.
If you have forgotten or neglected to file your taxes, it is possible to remove or reduce the penalty if you can show that you acted in good faith and can demonstrate reasonable cause to the IRS that you weren’t able to fulfill your tax obligations. You can make a request for penalty relief over the phone, or in writing using Form 843.
Many Americans living overseas either don’t realize or willfully neglect their tax filing obligations. Keep in mind that this can bear serious consequences. If you’re in this category, we recommend consulting a tax professional to help you get your taxes in order and apply for penalty relief on your behalf. We’ve expanded more on this topic at the end of this post.
Filing Too Early
While it may seem counterintuitive, filing your taxes too early can also put you at a disadvantage. If you file your taxes before you’ve received all of the proper documentation and forms regarding your income, or before certain relevant policies have come into effect, you may be missing out on possible tax benefits. Our recommendation is to wait until you have all of the necessary information needed to file your taxes completely and accurately.
You can follow our guide "A US Taxpayer's Field Guide: The Essential IRS Forms and Concepts" to collect the necessary documents for US tax filing to make sure you’re fully prepared.
If you happen to file too early and later realize that you missed some important information or made mistakes in your filing, it is possible to make amendments. See our section on amending your tax return below.
Paying Too Late
You may think it goes without saying, but it is essential that you do not miss the tax payment deadline if you owe taxes! Many people think that they can get away with not paying their taxes by simply not filing - but doing so makes the problem much worse. Late payment (especially intentionally late payments, or hiding taxable income) can result in serious fines and even criminal penalties.
Another common mistake is not understanding that your taxes are due on April 15 whether or not you request an extension! If you are self-employed or have other income that doesn’t have taxes withheld, you will need to make quarterly estimated tax payments as well. Estimating your tax payments is beyond the scope of this article, but more details can be found on the IRS website. We recommend consulting a professional if you think you fall into this category.
For taxpayers who cannot pay what they owe, there are options available to you. Payment plans are available, although the owed amount will accrue interest over time. The IRS can determine to delay collection if your financial situation makes you unable to pay (interest will still accrue).
If you’ve paid too late, and are being subjected to penalties, you can also seek penalty relief. See our notes on penalty relief above in the section on “Filing Too Late”.
Missing, or Inaccurate Personal Information
Another obvious, but all-too-common mistake that we see year after year is taxpayers making simple clerical errors on their tax paperwork. When filling out your tax forms, certain information needs to be absolutely 100% correct. This includes, but is not limited to the following:
Social Security Number
Names – your name must match with the name on your social security card.
Bank account numbers
Missing signatures
Be absolutely sure that these fields are filled correctly. Triple-check them!
Math or Calculation Errors
When filling out your Individual Income Tax return (1040) and other related forms, there are a lot of fields that require you to do some basic calculations. We are only human, and humans make mistakes. Whether you punched a wrong number into your calculator or forgot to carry a zero, it’s absolutely possible to make simple math blunders on your tax forms.
Making a small math error can have a big impact on your final tax liability, so don’t take it lightly. Triple check all of your calculations! You could be leaving money on the table, or worse, under-reporting your taxes – even honest mistakes can incur penalties and interest.
Using e-filing software or hiring a professional to help prepare your taxes are both good ways to reduce the occurrence of any numerical or clerical errors in your tax return.
Not planning ahead
You should prepare well in advance each year for filing your taxes. Keep all documents related to your income, assets, and other relevant information stored safely in one place where you can easily access them.
Advance preparation is the key to avoiding last-minute panic – and last-minute mistakes. If you filed your taxes last year, make a note of all the additional forms and schedules that you completed, and make sure you’re including them again (if necessary) this year.
Keep track of major life events (marriage, divorce, deaths in the family) as these all have an impact on your tax return. Our earlier guides "US Federal Tax Forms: What is Form 1040?" "US Federal Tax Forms: What is Form W-2 and Schedule K-1?", "US Federal Tax Forms: Form 1095-A, Filing Status, Investment Income and Property Sales", and "US Federal Taxes: Inheritance, Marriage, Expenses and Deductibles" to preparing your US tax return has a detailed breakdown of how these life events can affect your tax liability.
The upcoming article will disclose further information on incorrect filing status, claiming improper dependents or deductions, and misreporting income, common issues for many tax residents.
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