The answer to this question may actually surprise you. I have heard many myths over the years about what the answer to this question is. Throughout my career at the Internal Revenue Service, as a Revenue Officer I continually dealt with taxpayers that either owed the IRS back taxes, or had tax returns that they had not filed, or both.
Many of these folks could not understand why they had to pay so much interest and penalties when, for example, they paid their taxes on May 1st, only 2 weeks late? Part of my job as a Revenue Officer was to educate taxpayers about when taxes are lawfully due to be paid. Spoiler alert: It is not April 15th (or October 15th if you file an extension).
Federal income taxes are actually due to be paid when the money is paid. So, if you get paid every Friday, then your income taxes are due on that Friday. Which is why your employer withholds them from your check, and hopefully turns them over to the IRS as they are supposed to.
But what if you are self-employed? In that case, you may not pay yourself on any particular schedule. This is not uncommon among self-employed individuals. And, the IRS does not want self-employed taxpayers sending them checks on no particular schedule because it would be too labor-intensive to apply all of the payments correctly. Self-employed taxpayers must 1st: at the end of each quarter total up their gross profits, and 2nd: they must “estimate” the amount of taxes that they will owe the IRS based on that gross profit. Then they must pay the IRS that amount in order to stay current on this year’s taxes. Otherwise, they must pay an Estimated Tax penalty when they file their return for not paying their current taxes when they were legally due to be paid.
Also, if you are having withholding taken out of your check, or if you are self-employed and paying it yourself, make sure the amount is adequate to pay what you actually owe. Because if you do pay some money over to the IRS, and it’s not enough, you will also be penalized for this (Death and taxes, right?). You will get credit for these payments on your tax return when you file it.
So if you get a bill from the IRS about 6 weeks after you file your return for an Estimated Tax Penalty, well, now you know where you went wrong. You can get more detailed information about all of this at www.irs.gov. Use the search bar at the top right of the home page.