Handbook / Estimated tax

Underpayment penalty for estimated tax in the 2026 tax year: how it works and how to avoid it

Tax-year note: Tax information on this page applies to the 2026 tax year (returns filed in 2027), from IRS pages checked in November 2026. Figures and dates are labelled with their tax year where they appear. Check current IRS pages before you rely on them.

The underpayment penalty catches many people in their first year of self-employment. Nobody withheld tax from their client payments, they paid the bill in April, and then a penalty appeared. It is usually modest, but it is avoidable. This guide explains how the penalty works for the 2026 tax year, using the IRS penalty page, the IRS quarterly interest rate page and the 2026 Form 1040-ES, all checked in November 2026.

What triggers it

The US expects tax to be paid as income is earned. Employees do that through withholding. Self-employed people usually do it through estimated payments, on the dates set by the 2026 Form 1040-ES: April 15, June 15 and September 15, 2026, and January 15, 2027.

If, by any of those dates, your withholding plus estimated payments fall short of what was required for that installment, the IRS may charge the penalty for the shortfall.

How it is calculated

The IRS penalty page says the penalty is calculated based on:

• the amount of the underpayment
• the period when it was due and underpaid
• the published quarterly interest rate for underpayments

The tax used is the tax shown on your original return, or a later return filed by the due date, meaning total tax minus total refundable credits.

2026 rates. The IRS quarterly interest rate page lists the underpayment rate for non-corporate taxpayers in 2026 as 7% for January to March, 6% for April to June, 7% for July to September and 7% for October to December. Rates are set quarterly, so check the page for later periods.

Because it is time-based, a shortfall corrected a few weeks late costs much less than one left until April.

Example (2026 tax year): A consultant's required installment for June 15, 2026 was $2,000, and she paid nothing until August 14, 2026. The penalty on that installment is based on $2,000 underpaid for about two months at the published rates for those quarters. She pays the September 15 installment on time, and the shortfall stops growing once paid.

How to avoid it

The IRS penalty page says you may avoid the penalty if:

• your return shows you owe less than $1,000, or
• you paid at least the smaller of 90% of the current year's tax or 100% of the prior year's tax.

For the 2026 tax year, the 2026 Form 1040-ES says that if your 2025 AGI was more than $150,000 ($75,000 married filing separately), use 110% of your 2025 tax instead of 100%. The guide on the safe harbor turns these tests into a payment plan.

Ways to reduce it

The IRS lists situations where Form 2210 can help:

• Uneven income. If your income varies during the year, completing Form 2210 Schedule AI, the annualized income installment method, can reduce or eliminate the penalty for quarters when you earned less.
• Withholding timing. If most of your income tax was withheld early in the year rather than evenly, Form 2210 may also help.

Practical steps during the year:

1. Catch up quickly. If you miss an installment, pay as soon as you can.
2. Use withholding. If you or your spouse has wages, raising withholding through Form W-4 counts toward your payments.
3. Review mid-year. Compare your profit with the plan and adjust.

Waivers

The IRS says the penalty generally cannot be waived for reasonable cause. It may be removed or reduced if the underpayment resulted from a casualty, local disaster or other unusual circumstance where imposing it would be unfair. The IRS may also reduce it if you or your spouse retired in the past two years after reaching age 62, or became disabled, and had reasonable cause. The Instructions for Form 2210 explain how to request this.

When you get a notice

The IRS penalty page says it sends a notice if you owe the penalty. Read it, check it against your payment records, and respond by the date shown if you believe a waiver or Schedule AI calculation applies. Keep copies of what you send.

Make it routine

The penalty is mostly a planning problem. Four calendar dates, a set amount for each, and a tax savings account that receives a share of every payment you receive will prevent it in most years. The guide on Form 1040-ES covers how to pay.

For 2026, pay on time each quarter, aim for the safe harbor, catch up quickly if you fall short, and use Schedule AI if income was uneven.