How to Tell If Your Quarterly Estimated Taxes Are Wrong

Quarterly estimated payments exist because the U.S. tax system is pay-as-you-go — if you're self-employed or run a business, nobody withholds tax from your income automatically, so the IRS expects you to send in an estimate four times a year. The problem is that most business owners calculate that estimate once, usually based on last year's return, and then never look at it again until the following April.

That one-time calculation is the root of almost every quarterly tax problem we see. Income that grows during the year means the estimate is too low, and an underpayment penalty is quietly building. Income that drops, or a year where expenses were unusually high, means the estimate is too high, and cash that could be sitting in your business is sitting with the IRS instead until you file.

The IRS gives you a legal safe harbor to avoid a penalty: pay at least 90% of the current year's actual tax liability, or 100% of last year's liability (110% if last year's adjusted gross income was over $150,000), whichever is smaller. Most people default to the 100%-of-last-year option because it's the easiest to calculate in January — but 'easiest to calculate' and 'accurate for a growing or changing business' are two different things.

A simple check you can do yourself: pull your year-to-date profit and loss statement partway through the year and compare it, proportionally, to what you assumed when you set your estimate. If your actual year-to-date profit is running well ahead of or behind the pace implied by your original estimate, the payment you're about to send is very likely wrong in one direction or the other.

The harder part isn't spotting that something's off — it's recalculating correctly. That means accounting for depreciation elections, entity structure, retirement contributions, and any deductions specific to your industry, not just scaling last year's number up or down. That's the recalculation we do every quarter for clients, specifically so this doesn't get caught once a year by accident.