Estate Tax Installment Payment — Section 6166 Deferral for Family Business Estates
Federal estate tax is due nine months after death — a tight deadline that creates severe liquidity problems when the estate consists largely of a closely held business that can't easily be liquidated without destroying value. A family farm, a manufacturing company, a professional practice, or a real estate business may be worth millions on paper but generate no cash that can be quickly converted to pay a multi-million-dollar estate tax bill. Section 6166 of the tax code provides an important relief valve: if more than 35% of the adjusted gross estate consists of an interest in a closely held business, the executor can elect to defer payment of the estate tax attributable to that business interest for up to 5 years (interest-only payments during the deferral period) and then pay the deferred tax in up to 10 equal annual installments. Combined with a special low interest rate of 2% on a portion of the deferred tax, § 6166 can allow a family to retain and continue operating a business without a forced sale to pay estate taxes.
Current Law (2026)
| Parameter | Value |
|---|---|
| Core statute | 26 U.S.C. § 6166 |
| Eligibility threshold | Value of closely held business interest must exceed 35% of the adjusted gross estate |
| Maximum deferral period | 5 years of interest-only payments before first installment, then 10 annual installments = up to 14 years total (10 installment payments begin 5 years after normal estate tax due date) |
| Amount eligible for deferral | The portion of estate tax attributable to the closely held business interest (not the full estate tax) |
| Interest rate on deferred tax | 2% on deferred tax attributable to the first $1,700,000 (2026, indexed) of the closely held business value above the estate tax exemption; 45% of the federal underpayment rate on the remainder |
| "Closely held business" definition | Proprietorship; partnership (≥20% of total capital or ≤45 partners); corporation (≥20% of voting stock or ≤45 shareholders) |
| Acceleration triggers | Distribution or disposition of 50%+ of the closely held business interest; failure to make an installment payment; certain ownership changes |
| Alternative: § 303 stock redemption | Corporations can redeem enough stock to cover estate tax without it being treated as a dividend |
Legal Authority
- 26 U.S.C. § 6166(a)(1) — Election available if the closely held business interest exceeds 35% of adjusted gross estate; executor may elect to pay estate tax in 2-10 installments
- 26 U.S.C. § 6166(a)(2)-(3) — Maximum amount eligible for installment payment: the ratio of the closely held business amount to the adjusted gross estate, applied to the total estate tax; first installment due not more than 5 years after the normal § 6151(a) due date
- 26 U.S.C. § 6166(b)(1) — Definition of closely held business: proprietorship; partnership with ≥20% capital interest or ≤45 partners; corporation with ≥20% voting stock or ≤45 shareholders
- 26 U.S.C. § 6166(b)(8) — Aggregation: if the decedent held interests in multiple closely held businesses, they may be aggregated if the decedent had a ≥20% interest in each — allowing estates with several minority business interests to meet the 35% threshold collectively
- 26 U.S.C. § 6166(g) — Acceleration: the entire unpaid tax becomes due immediately if the closely held business interest is sold or otherwise disposed of (≥50%), if an installment payment is not made when due, or in other specified events; like a note called due
- 26 U.S.C. § 6601(j) — The 2% interest rate: the portion of deferred estate tax attributable to the first $1,700,000 (inflation-adjusted; §6601(j)(3)) of closely held business value above the estate tax exemption bears interest at only 2% per year — a subsidized rate designed to preserve family businesses
How the 35% Test Works
The first hurdle is meeting the 35% threshold: the value of the closely held business interest(s) included in the gross estate must exceed 35% of the "adjusted gross estate" — the gross estate minus deductible expenses, debts, losses, and charitable bequests.
Example: Estate worth $10 million gross; $1 million in debts and deductible expenses. Adjusted gross estate = $9 million. Family farm valued at $4 million. Farm is 44.4% of adjusted gross estate — exceeds 35%, § 6166 election available.
Aggregation of multiple interests: If the decedent held interests in several closely held businesses, § 6166(b)(8) allows aggregating the values if the decedent had a 20%+ interest in each. A decedent with 30% in a small manufacturing company ($2M), 25% in a family partnership ($1.5M), and 22% in a rental real estate LLC ($1.5M) can potentially aggregate all three ($5M total) to meet the 35% test.
The Payment Schedule
Once the § 6166 election is made, the estate pays interest-only for up to 5 years from the date the estate tax was originally due (9 months after death). Then, equal annual installments of the principal begin and continue for up to 10 years.
Timeline example: Death in January 2026. Estate tax normally due October 2026. With § 6166 election and 5-year deferral:
- October 2026 through October 2030: interest-only payments annually (5 years)
- October 2031: first principal installment (1/10 of deferred tax)
- October 2032 through October 2040: 9 more annual installments
- Total deferral period: up to 14 years after the estate tax due date
The 2% interest rate benefit: On deferred tax attributable to the first $1,700,000 (2026) of closely held business value above the estate tax exemption, the interest rate is only 2%. This is a substantial subsidy — the normal IRS underpayment rate in 2026 is approximately 8%, so the 2% rate saves families real money on the carrying cost of the deferred tax. On amounts above the $1,700,000 threshold, the interest rate is 45% of the regular underpayment rate (currently ~3.6%).
Acceleration: When Deferral Ends Early
The installment arrangement terminates and all remaining deferred tax becomes immediately due if:
- The business interest is sold or distributed and the disposition represents 50% or more of the interest
- An installment payment or interest payment is not made on time
- The closely held business interest loses its character (partnership terminates, corporation liquidates, etc.)
- Underpayment occurs due to fraud
Planning implication: Transferring or selling more than half of the business interest during the installment period terminates the § 6166 election — a critical constraint for families who want to use § 6166 AND gradually transition ownership to the next generation or sell to a third party.
How It Affects You
<!-- pria:personalize type="impact" -->If you're inheriting a family farm or closely held business: Act before the estate tax deadline. The § 6166 election is made on Form 706 (United States Estate Tax Return), which is due 9 months after the date of death — for a January 2026 death, that's October 2026. You can file for a 6-month extension to file (Form 4768), pushing the deadline to April 2027, but the estate tax payment is still due at 9 months unless you've elected the extension. The § 6166 election must be included with the Form 706 when it's filed — it cannot be added later as an amended return. Missing this window permanently forfeits the installment option. Attach a statement identifying the closely held business interest, its value, the percentage of the adjusted gross estate it represents, and the number of installments elected (2-10). Work with an estate attorney who does this regularly — the aggregation rules (§ 6166(b)(8)) and the calculation of the eligible deferred amount are technical enough that errors on the Form 706 are common.
If you're doing pre-death planning around the 35% test: The threshold is based on the closely held business interest as a percentage of the adjusted gross estate — the gross estate minus debts, deductible expenses, and charitable bequests. If the business makes up 30% of the estate and you're trying to reach 35%, two planning levers exist: (1) reduce non-business assets through gifting (gifts made before death reduce the gross estate, but watch the gift tax implications); (2) use § 6166(b)(8) aggregation — if you have minority interests in multiple businesses (say, 25% in a manufacturing company, 30% in a family partnership), they can be combined to meet the 35% test if the decedent held ≥20% in each. Note that the interaction with § 2032A special use valuation is counter-intuitive: § 2032A reduces the farm's value in the estate, which can actually help or hurt the 35% test depending on the numbers — model both elections together with your estate attorney.
If you're weighing whether to use § 6166 or pay upfront: The 2% interest rate on the first $1,700,000 (2026) of eligible deferred tax is a genuine subsidy — 2% is far below any commercial borrowing rate when the IRS's normal underpayment rate is 8%. On $500,000 of tax at the 2% rate, you pay $10,000/year in interest versus $40,000/year at market rates. For the portion of deferred tax above the $1,700,000 threshold, the interest rate is 45% of the regular underpayment rate — approximately 3.6% in 2026 — still below typical commercial rates. The comparison: if the estate can borrow to pay the tax at 6-7%, using § 6166 at 2-3.6% is almost always preferable. If the business generates sufficient cash flow to fund installments from operations, § 6166 is clearly the right call.
If you're planning for business succession with § 6166 in place: The 50% disposition trigger is a planning constraint that must be communicated clearly to all family members. If the plan involves gradual sale of the business to the next generation — annual transfers of ownership interest — confirm that each transfer stays below the 50% cumulative threshold that triggers acceleration. For example, transferring 30% of a business interest in year 3 of the § 6166 period is fine; transferring another 25% (totaling 55% since the election) triggers immediate acceleration of all remaining deferred tax. Structure any ownership transitions with the § 6166 acceleration rules explicitly in mind, and coordinate with the estate attorney before each transfer.
<!-- /pria:personalize -->State Variations
Several states have estate taxes with their own deferral provisions for closely held business interests, modeled on § 6166. New York allows installment payments for qualifying closely held business interests in the New York estate. Massachusetts has a similar provision. States without estate taxes (most states no longer impose an estate tax; only about 12 states and DC still have one) have no comparable provision needed.
Pending Legislation
The federal estate tax exemption amount is scheduled to revert from its current $13.61 million per person to approximately $7 million (inflation-adjusted) after December 31, 2025, unless Congress acts. This potential "sunset" would dramatically increase the number of estates subject to estate tax, and consequently the number for whom § 6166 becomes relevant. The 2% interest rate threshold ($1,700,000) is indexed for inflation annually.
Recent Developments
The IRS has issued guidance clarifying the aggregation rules under § 6166(b)(8) for closely held business interests, and the rules for what constitutes a "disposition" that triggers acceleration. The Tax Court has decided several cases addressing whether specific assets qualify as interests in a closely held business for § 6166 purposes — in particular, whether real estate holding entities qualify (they can, if the entity is actively managing the property rather than simply passively holding it). With the potential TCJA sunset reducing the estate tax exemption, § 6166 planning has become increasingly important in estate planning discussions.