IRC 6166 estate tax deferral lets an executor stretch the federal estate tax tied to a closely held business interest over as long as 14 years instead of paying it within nine months of death. The deferral does not reduce the tax; it buys the business time to generate the cash to cover the bill. To use it, the business must be an active trade or business, the decedent must have held a qualifying ownership stake, and the interest must make up more than 35% of the adjusted gross estate.
Which Business Interests Qualify
The business has to actually do something. Companies with employees delivering services, manufacturing products, or running daily operations qualify. Entities that passively hold assets — triple-net lease properties, marketable securities, raw land — generally do not.
Three legal forms are eligible: a sole proprietorship, a partnership interest, or corporate stock. Each must also meet at least one of two ownership tests that define “closely held”:1Office of the Law Revision Counsel. 26 US Code 6166 – Extension of Time for Payment of Estate Tax Where Estate Consists Largely of Interest in Closely Held Business
- The gross estate includes at least 20% of the partnership’s total capital interest, or 20% or more in value of the corporation’s voting stock.
- The partnership has 45 or fewer partners, or the corporation has 45 or fewer shareholders.
Either test is enough. A sole proprietorship clears both by default.
If the decedent’s personal holdings fall short, the family attribution rule can rescue the election. Interests held by the decedent’s spouse, children, grandchildren, and parents are treated as if the decedent owned them directly for purposes of the ownership thresholds.1Office of the Law Revision Counsel. 26 US Code 6166 – Extension of Time for Payment of Estate Tax Where Estate Consists Largely of Interest in Closely Held Business
Passive Assets Get Stripped Out
Even in a qualifying operating company, the value of any passive assets is removed before the business interest is measured. Passive assets include excess cash in investment accounts, unrelated rental property, and stock in another company.1Office of the Law Revision Counsel. 26 US Code 6166 – Extension of Time for Payment of Estate Tax Where Estate Consists Largely of Interest in Closely Held Business Stock in a subsidiary is treated as passive unless the parent owns at least 20% of the subsidiary’s voting stock (or the subsidiary has 45 or fewer shareholders) and at least 80% of each company’s assets are used in active operations.
A business worth $10 million on paper that holds $3 million in passive investments has only $7 million of qualifying value. That reduced figure drives both the 35% test and the maximum amount of tax that can actually be deferred.
The 35% Threshold
The qualifying interest must exceed 35% of the adjusted gross estate. The adjusted gross estate equals the gross estate minus deductions for debts, administration expenses, funeral costs, and casualty losses under IRC Sections 2053 and 2054.2Legal Information Institute. 26 US Code 6166(b)(6) – Adjusted Gross Estate Definition Values are the ones used for estate tax purposes, either date-of-death or alternate valuation date.
The margin is often tight. Higher-than-expected executor fees or a modest downward valuation adjustment on the business can push the ratio under 35% and eliminate the deferral entirely. There is no partial credit.
If no single business clears 35%, an estate can combine interests in multiple businesses to meet it. Aggregation only works when the gross estate holds at least 20% of each business being combined.1Office of the Law Revision Counsel. 26 US Code 6166 – Extension of Time for Payment of Estate Tax Where Estate Consists Largely of Interest in Closely Held Business A smaller stake cannot be added, even if the pool would otherwise clear the threshold.
How to Make the Election
There is no dedicated IRS form. The executor attaches a notice to a timely filed Form 706 identifying the decedent, stating the value of the gross estate and the closely held business interest, specifying the amount of tax to be deferred, and indicating how many annual installments are being elected (between two and ten).1Office of the Law Revision Counsel. 26 US Code 6166 – Extension of Time for Payment of Estate Tax Where Estate Consists Largely of Interest in Closely Held Business The deadline is the Form 706 due date including any extension, generally nine months after death plus a six-month extension.3Internal Revenue Service. Filing Estate and Gift Tax Returns
Miss that deadline and the election is gone. The IRS enforces it strictly.
Only the portion of estate tax attributable to the qualifying business interest can be deferred. If the business represents 40% of the adjusted gross estate, 40% of the net estate tax goes on installments; the other 60% is due with the return.
When Qualification Is Uncertain, File a Protective Election
If a valuation is in dispute and the estate might or might not clear 35% once the numbers settle, a protective election preserves the right to defer. The executor files it with the timely Form 706, stating that the election depends on final determined values meeting the threshold. Once final values are set — often after an audit — the executor perfects the election by notifying the IRS of the final tax liability and the required details within 60 days. Without that protective filing, an estate that only qualifies after audit loses the deferral.
The 14-Year Payment Timeline
The deferral has two phases. For up to five years after the original estate tax due date, the estate pays interest only — no principal. The executor picks when the first principal installment lands, any date up to five years out.1Office of the Law Revision Counsel. 26 US Code 6166 – Extension of Time for Payment of Estate Tax Where Estate Consists Largely of Interest in Closely Held Business After that, principal plus interest comes due in equal annual installments for up to ten years. Stretched to the limit, that is five years of interest-only payments followed by ten years of combined payments, totaling 14 years.
Interest Rates on the Deferred Tax
The deferred tax is split into two slices with different interest rates.
A fixed 2% rate applies to the “2-percent portion.” That amount is calculated by running the estate tax rate schedule on a base equal to an inflation-adjusted $1 million threshold plus the applicable exclusion, then subtracting the applicable credit. In rough terms, the 2% rate covers the tax generated by the first $1 million (inflation-adjusted) of taxable business value above the exemption.4Office of the Law Revision Counsel. 26 USC 6601 – Interest on Underpayment, Nonpayment, or Extensions of Time for Payment, of Tax For 2025 decedents, the inflation-adjusted threshold in that formula is $1,900,000.5Internal Revenue Service. Revenue Procedure 2024-40
Deferred tax above the 2-percent portion carries interest at 45% of the standard IRS underpayment rate, which fluctuates quarterly.6Internal Revenue Service. Revenue Procedure 98-15 If the underpayment rate is 8%, this slice carries interest at 3.6%.
One catch: interest on both portions is non-deductible for income tax purposes. It is a straight financing cost with no offsetting tax benefit. Interest accrues annually and must be paid each year, including during the five-year interest-only phase.
What Can Terminate the Deferral
The installment privilege can collapse early, and the triggers deserve careful attention because termination means the entire unpaid balance comes due on demand.
Selling Off the Business
If the combined value of dispositions (sales, exchanges, distributions) and withdrawals of money or property from the business reaches 50% or more of the qualifying interest’s value, the full remaining tax is due immediately.1Office of the Law Revision Counsel. 26 US Code 6166 – Extension of Time for Payment of Estate Tax Where Estate Consists Largely of Interest in Closely Held Business The threshold is measured against the originally qualifying value, not current market value.
Several routine events are exempt. Distributing the business interest to the heir entitled to it under the will or applicable law does not count, and the exemption carries through subsequent transfers within the family. Section 303 stock redemptions used to pay estate taxes and expenses are also excluded, subject to specific conditions. Tax-free corporate reorganizations and qualifying spinoffs do not trigger acceleration, and the stock received in the exchange is treated as qualifying interest going forward.
Missing a Payment
A missed principal or interest payment triggers acceleration. The estate has a six-month cure window, but curing is expensive: the favorable 2% and reduced rates no longer apply to the late amount, and a penalty equal to 5% of the overdue payment accrues for each month or partial month the payment is late.1Office of the Law Revision Counsel. 26 US Code 6166 – Extension of Time for Payment of Estate Tax Where Estate Consists Largely of Interest in Closely Held Business After six months without payment, the full balance accelerates.
Undistributed Net Income
Starting with the tax year that ends on or after the first principal installment date, the estate must apply its undistributed net income toward the deferred tax balance. That figure is distributable net income under IRC 643 minus amounts distributed to beneficiaries, income tax paid by the estate, and estate tax paid that year.1Office of the Law Revision Counsel. 26 US Code 6166 – Extension of Time for Payment of Estate Tax Where Estate Consists Largely of Interest in Closely Held Business The payment is due with the income tax return for that year, and failing to make it is treated like missing a scheduled installment.
Securing the Deferred Tax
Because the government is extending credit for up to 14 years, it wants assurance of collection. The executor has two options.
The first is a special lien under IRC 6324A. The lien attaches to property expected to satisfy the deferred tax plus projected interest and takes the place of a surety bond.7Office of the Law Revision Counsel. 26 US Code 6324A – Special Lien for Estate Tax Deferred Under Section 6166 Everyone with an interest in the liened property must sign the agreement. The property is encumbered, but the estate avoids ongoing out-of-pocket cost.
The alternative is a surety bond. Premiums typically run in the low single-digit percentages of the deferred amount per year, varying by the estate’s risk profile and the bonding company. Over 14 years on a large balance, cumulative premiums can eat meaningfully into the benefit of the deferral. Failure to provide adequate security when the IRS asks for it can itself terminate the installment privilege.
If the IRS Denies or Terminates the Election
The IRS issues a formal determination letter when it denies an election (Letter 3571) or rules that an existing election has ended (Letter 3570). Before going to court, the estate must exhaust administrative remedies, which includes requesting a conference with IRS Appeals after a preliminary determination.8Internal Revenue Service. Revenue Procedure 2005-33
If appeals fail, or if the IRS does not act on a determination request within 180 days, the estate can petition the U.S. Tax Court for a declaratory judgment under IRC 7479. The Tax Court can rule on whether the initial election was valid and whether an existing election should continue. Exhaustion is deemed satisfied after 180 days of IRS inaction, provided the estate took all reasonable steps to obtain a determination.8Internal Revenue Service. Revenue Procedure 2005-33
The stakes justify the procedure. Losing a 6166 election means the deferred balance comes due immediately, and a business built around the assumption of a 14-year payment schedule may not survive that demand. Filing a protective election at the outset, keeping meticulous records of active business operations, and responding promptly to IRS inquiries are the practical defenses against ever reaching that point.