The Third Estimated Tax Instalment for 2026 Falls Today. Above $150,000 of Prior-Year Income, the Safe Harbour Is 110%, Not 100%.

The United States collects income tax as income is earned, not once a year. For wage earners that happens through withholding. For everyone whose income arrives without a payroll department attached to it - the self-employed, partners, S corporation shareholders, landlords, people living on investment income - it happens through four estimated tax payments. The third one for 2026 is due today.

The four dates

Form 1040-ES for 2026 lists them: April 15, 2026; June 15, 2026; September 15, 2026; and January 15, 2027. The periods they cover are not equal quarters, which is the first thing that surprises people who assume the schedule is evenly spaced.

Who the rule reaches

Two conditions have to hold together. The IRS states the first as a dollar threshold.

You expect to owe at least $1,000 in tax for 2026, after subtracting your withholding and refundable credits.

The second is that withholding and refundable credits are expected to come in below the smaller of two tests. Corporations have their own threshold: the IRS says they generally have to make estimated payments if they expect to owe $500 or more.

The two tests

1. 90% of the tax to be shown on the 2026 return, or
2. 100% of the tax shown on the 2025 return.

The smaller of those two figures is the target. The second test is the one most people rely on, because last year's tax is a known number and this year's is not.

The higher-income substitution

Above an income line, the prior-year safe harbour gets more expensive.

If your adjusted gross income (AGI) for 2025 was more than $150,000 ($75,000 if your filing status for 2026 is married filing separately), substitute 110% for 100%.

The form notes this substitution does not apply to taxpayers with two-thirds or more of their income from farming or fishing, who are covered by separate rules.

What happens if a payment is short or late

The form puts it plainly: if payments are late or not large enough, a penalty for underpaying may be charged. The penalty is computed on Form 2210 for individuals and Form 2220 for corporations. It is calculated period by period, which is why a large payment in January does not necessarily cure a shortfall from September.

Paying it

The IRS reminded taxpayers on September 10, in release IR-2026-109, that Direct Pay accepts estimated tax payments from a checking or savings account without fees or registration. Payments can be made the same day or scheduled up to 365 days ahead, changed or cancelled up to two business days before the scheduled date, and are capped at under $10 million per transaction. Individuals can also use it for balance due, amended return and extension payments.

Direct Pay gives taxpayers a free, secure, and convenient way to pay directly from a bank account.

This article describes published filing mechanics and is not tax advice. Individual circumstances vary and a qualified tax professional can address them.