The tax on your sale can come due before April

Yes, in most cases. Gain on the sale of your company is income nobody withholds against, and federal tax on it comes due in installments during the sale year, not in April. Section 6654 adds an amount to the tax when installments are missed. One safe harbor can legitimately defer most of the payment.

Do I need to make estimated tax payments after selling my business?

Usually yes. Federal income tax is pay-as-you-go. Gain on a sale reaches you with no payroll department withholding against it, and a buyer sends no federal income tax deposit on a domestic seller’s price. Section 6654 imposes an addition to tax on an individual who underpays any required installment, even where the balance is paid with the return.

The structure matters more than the label. It is not a fine for filing late, and an extension to file neither forgives nor postpones it. It is computed installment by installment, each period running from the missed due date to the earlier of payment or April 15 following the close of the tax year. The rate is the federal underpayment rate, reset quarterly under section 6621: 7 percent for individuals for the quarter beginning October 1, 2026. The Internal Revenue Manual states the addition is not interest, but is computed in the same manner, except that it is not compounded daily.

The statutory escapes are narrow. No addition applies if the tax shown on the return, reduced by the section 31 withholding credit, is less than $1,000. None applies if you had no tax liability for the preceding year, but only if that year ran a full twelve months and you were a United States citizen or resident throughout it. Neither describes a seller who just closed a deal. Section 6654(e)(3) adds a waiver for casualty, disaster, or other unusual circumstances, and for a taxpayer who retired after reaching age 62 or became disabled where the underpayment was due to reasonable cause. That one is discretionary, requested on Form 2210, granted or refused on the facts.

Law: 26 U.S.C. 6654(a), (b)(2), (e)(1)-(3), 31, 6621; IRM 20.1.3.

What are the four estimated tax due dates, and how much is each one?

Section 6654(c) sets four required installments for each taxable year, due April 15, June 15, September 15, and January 15 of the following year. Section 6654(d)(1)(A) makes each installment 25 percent of the required annual payment. Section 6654(d)(1)(B) defines that payment as the lesser of 90 percent of the current year’s tax or 100 percent of the prior year’s.

Dates landing on a weekend or holiday move to the next business day (section 7503). Four features surprise sellers.

• The periods are not even quarters. The second installment covers two months. The fourth covers four.
• The last installment falls on January 15 of the following year. A December closing produces a payment obligation about thirty days later, not in April.
• Section 6654(h) removes the addition on the fourth installment only if you both file the return and pay the full amount shown on it by January 31. For 2026 the IRS states that date as February 1, 2027. A partial payment does not qualify, and filing a complete return a month after a December closing is rarely realistic.
• Section 6654(b)(3) credits payments against unpaid installments in the order they were due. A catch-up payment in September does not land on the September installment first. It fills April, then June, while the clock on the earliest shortfall keeps running.

Law: 26 U.S.C. 6654(b)(3), (c), (d)(1)(A)-(B), (h), 7503; IRS Form 1040-ES (2026).

Can I pay installments based on last year’s tax and pay the sale tax in April?

Often, yes. The prior-year safe harbor in section 6654(d)(1)(B) makes the required annual payment the lesser of 90 percent of the sale year’s tax or 100 percent of the prior year’s tax. A seller whose prior year was modest can pay four installments measured against that modest year and settle the sale tax with the return.

Two limits sit in the same subparagraph. The prior-year prong is unavailable if you filed no return for the preceding year, or if that year was not twelve months. And section 6654(d)(1)(C) substitutes 110 percent for 100 percent where the adjusted gross income shown on the prior year’s return exceeded $150,000, or $75,000 for a married taxpayer filing separately. Those figures sit in the statute as of October 2026 and are not indexed for inflation.

I read the prior year’s filed return before I read the letter of intent, because the number that governs the installments is already fixed and the deal price is not.

The safe harbor has no partial credit. It protects you only if every installment is paid in full and on time. Three correct payments and one missed payment is not substantial compliance. It is one underpaid installment, and the ordering rule fills it last.

The prior-year safe harbor is a floor with no tolerance. Hit it four times and the sale tax waits for April. Miss it once and the exposure starts at that date.

Law: 26 U.S.C. 6654(b)(3), (d)(1)(B), (d)(1)(C).

My deal closed in November. Do I have to pay as though I earned the gain in January?

No. The annualized income installment method in section 6654(d)(2) measures each required installment against income actually realized in the months of the year ending before that installment’s due date. A seller who closes late in the year can reduce the earlier installments and carry the burden in the period the gain arrived.

The method is run on Schedule AI of Form 2210, over periods ending March 31, May 31, August 31, and December 31. You compute income for each period, annualize it, compute the tax, and reduce each installment to what the period supports. All four get computed. The instructions to Form 2210 name a large capital gain late in the year as a reason to use it.

Three consequences follow. Annualizing does not erase the tax: whatever a reduced installment drops below 25 percent is added back to the later ones, so the money must be there on September 15 or January 15. A late closing stays inside the final period, so a November or December sale lands on January 15, not April. And the method is retrospective. You prove on a filed form that your income was back-loaded, which takes records of when the gain was realized: for a stock sale, the closing date; for an asset sale, the section 1060 allocation and the timing of each item.

Law: 26 U.S.C. 6654(d)(2), 1060; IRS Instructions for Form 2210 (2025), Schedule AI.

I am still on the company payroll. Can extra withholding fix an earlier shortfall?

Often, yes. Section 6654(g)(1) deems wage withholding to be estimated tax paid in equal parts on each of the four installment due dates, unless you establish the dates amounts were actually withheld. Withholding increased in November is therefore treated, by default, as if one quarter of it had been paid on April 15. Estimated tax payments get no such treatment.

That is a real tool for an owner who stays an employee through closing or under a transition services arrangement, and it has limits. It reaches only amounts actually withheld from wages and paid over, it needs a new Form W-4 and enough remaining payroll to carry the number, and it ends when the payroll does.

The default cuts both ways. It helps when withholding comes late. It hurts when withholding came early and you want credit on the first installment, where you must establish the actual dates.

A dollar of estimated tax is credited when paid. A dollar of wage withholding is credited as if a quarter had been paid in April. That asymmetry is the point.

Law: 26 U.S.C. 6654(g)(1)-(2), 31.

What if the buyer pays me over time, in an installment note or an earn-out?

Deferred consideration moves the question into every year a payment arrives. Section 6654 is an annual computation. It applies separately to each taxable year, against that year’s tax, with its own four installments and its own prior-year safe harbor measured by the year before. A payment stream is not one tax event. It is a sequence of them.

That has an edge. The year after a large closing your prior-year tax is enormous, so the prior-year safe harbor becomes the expensive option rather than the cheap one. In year two the 90 percent prong, or annualization, is usually the one to run.

How the gain is reported depends on the deal structure and on elections made with the return. The installment method lives in section 453, and electing out is done on a timely filed return, which pulls the whole gain into the sale year and with it that year’s installments. Reporting and funding are different problems, and the first sets the second.

Law: 26 U.S.C. 453, 6654(d)(1)(B).

My company is a C corporation. Does the company owe estimated tax too?

A C corporation has its own estimated tax regime under section 6655, separate from anything its shareholders owe, with installments due on the 15th day of the fourth, sixth, ninth, and twelfth months of its taxable year. The corporate prior-year exception is tighter than the individual one, and it nearly closes for a large corporation.

Read the definition before assuming it reaches you. A large corporation under section 6655(g)(2) is one with taxable income of $1,000,000 or more in any of the three taxable years immediately preceding the year in question. The test looks backward, so a company whose first seven-figure year is the sale year is generally not a large corporation for that year. It often becomes one the next year. Such a corporation may use prior-year tax for the first installment only, and the amount shaved off is added back to the second.

That matters in an asset sale out of a C corporation, where the corporation recognizes gain and the shareholders are taxed again on distribution. Both levels need projecting. Only one is yours.

Law: 26 U.S.C. 6655(c), (d)(1)-(2), (g)(2); IRM 20.1.3.

Does my state have its own estimated tax rules?

State estimated tax is a separate system from the federal one, and the federal safe harbors do not carry over. Most states with an income tax run their own installment regime, with their own due dates, prior-year rules, and penalty. A seller who funds the federal estimate correctly and ignores the state has solved half the problem.

Two issues recur in sales of pass-through entities. A partnership or S corporation with nonresident owners may have to withhold on, or file composite returns for, income sourced to that state. And gain can be sourced to a state where you do not live, pulling you into a nonresident filing. As of October 2026 these rules vary by state and change often, and nothing here states any state’s law. Put it to your accountant with the states named, before closing.

What should I do before the closing wire lands?

Three things protect a seller: a tax projection produced before closing rather than after, cash set aside from the wire itself, and the four installment dates on the calendar from the day the deal signs. The list below is the working version.

• Get a written projection before signing, showing federal tax on the gain, state tax, and the required annual payment computed both ways.
• Pull the prior year’s filed return. Its total tax and AGI lines set your floor.
• Move the estimated tax out of the proceeds on the day of funding, into a separate account.
• Calendar April 15, June 15, September 15, and January 15, with reminders a week early. The ordering rule punishes the first miss.
• Choose between the safe harbor and annualization once. A late-year closing points to Schedule AI, an early one to the safe harbor.
• Ask about raising wage withholding before year end if you are still on payroll, and re-run the analysis for next year if any consideration is deferred.

I ask for the projection before I ask what the buyer is offering, because a number not yet reduced by tax is not a number you can plan around.

The rules here do move. The What’s New section of the 2025 instructions to Form 2210 points to Notice 2026-3, which gives limited relief from part of the section 6654 addition attributable to a qualified sale of qualified farmland property to a qualified farmer where a section 1062(a) election is made. Nothing general excuses a seller from the four dates. All of this is stated as of October 2026; confirm the figures before you rely on them.

Law: 26 U.S.C. 6654; IRS Publication 505.