Having a financially successful year is certainly a good thing. But earning more money can also create an unexpected tax problem when the additional income hasn't been matched with sufficient tax payments.
This is especially important for business owners, self-employed individuals, taxpayers with multiple sources of income, and retirees taking additional distributions from retirement accounts.
The problem isn't necessarily that the taxpayer made a mistake. It's that the tax payments established at the beginning of the year may no longer reflect the taxpayer's actual circumstances.
Why Your Tax Payments May No Longer Be Enough
Federal income taxes generally operate on a pay-as-you-go system. Rather than paying everything when filing an annual return, taxpayers ordinarily pay throughout the year through withholding, estimated payments, or both.
For employees, federal income tax withholding generally occurs through payroll.
But additional income may not have sufficient withholding. Common examples include self-employment earnings, business profits, taxable investment income, and some retirement distributions.
For example, someone who earns a regular salary but develops a profitable side business may discover that the withholding from their paycheck doesn't cover the additional federal income tax and self-employment tax.
That's why income changes deserve attention before tax season.
Understanding the Estimated-Tax Safe Harbor
The IRS generally provides ways to avoid an estimated-tax underpayment penalty when required payments are made on time.
For many individual taxpayers, the required annual payment is based on the lesser of:
90% of the current year's tax, or
100% of the previous year's tax, provided the previous return covered a full 12 months.
For certain higher-income taxpayers, the prior-year percentage increases to 110%. Generally, this applies when the previous year's adjusted gross income exceeded $150,000, or $75,000 for married taxpayers filing separately.
Other special rules and exceptions can apply.
These are often called safe-harbor rules. They help determine whether enough tax has been paid to avoid an underpayment penalty.
However, meeting a safe harbor does not eliminate the actual tax liability. A taxpayer may still owe a substantial balance when filing the return.
For additional detail, see IRS Publication 505, Tax Withholding and Estimated Tax.
Why Timing Matters
For the 2026 tax year, the fourth federal estimated-tax installment is generally due January 15, 2027.
That doesn't mean every taxpayer can wait until January and automatically avoid an underpayment penalty.
Estimated-tax penalties are generally evaluated by payment period. Making a larger payment in the fourth quarter may not cure an earlier installment shortfall.
There is also an important difference between estimated payments and federal income tax withholding.
Withholding is generally treated as paid evenly throughout the year for estimated-tax purposes, unless the taxpayer uses the actual withholding dates. Because of this treatment, additional withholding late in the year may sometimes be useful when reviewing an underpayment situation.
Taxpayers whose income arrived unevenly may also benefit from reviewing the annualized income installment method.
The correct approach depends on the timing of the income, prior payments, projected tax, and other factors.
A Practical Example
Assume a married couple has regular W-2 earnings, and one spouse begins consulting during the year.
By November, the consulting activity has generated $30,000 of net business income.
The couple may have made no estimated payments because their regular jobs already withheld federal income tax.
However, the consulting profit may increase both income tax and self-employment tax.
Rather than simply waiting until April, they should project their 2026 tax liability, compare it with withholding and estimated payments already made, and determine whether an adjustment is appropriate.
This is a hypothetical example. The tax outcome depends on the couple's complete financial circumstances.
What to Review Before December 31
An effective year-end tax review should include current pay statements, year-to-date business profit, investment gains, retirement distributions, tax payments, and anticipated deductions and credits.
It should also identify significant changes in family circumstances, income sources, or business activity.
Sometimes the review identifies a need for additional withholding or estimated payments. Other times, the existing payments are adequate under the applicable rules.
The objective is to make an informed decision rather than simply assume the previous year's tax payments remain sufficient.
Planning Ahead With Alliance
At Alliance Financial & Income Tax, our approach is to review the tax consequences of important financial decisions before the year ends whenever possible.
If your income has changed substantially, our proactive tax-planning services can help you evaluate the effects on withholding, estimated taxes, and your broader tax situation.
You can also schedule an appointment with Alliance to discuss your year-end planning questions.
Good tax planning isn't necessarily about eliminating a tax bill. It's about understanding the rules, evaluating available options, and avoiding unnecessary surprises.
This article is general educational information and is not individualized tax or legal advice.