What an executor actually works through, and then the arithmetic on the installment test.
Size the obligation. Federal estate tax where any is owed, state death taxes, debts, funeral costs and administration expenses, against a due date nine months after the death.
Inventory what can be turned into cash by that date, and at what discount. A minority interest in a family business usually cannot be sold at all in that window.
Test the 35 percent thresholds. Section 6166 measures a closely held business interest against the adjusted gross estate; section 303 measures all of one corporation's stock against the same denominator.
Make the elections on the return. Section 6166 requires the election on a timely filed return; a section 6161 extension is a request for discretionary relief.
Protect the deferral afterwards. Watch the 50 percent disposition-and-withdrawal test for as long as installments run, and use the section 303 carve-out rather than an unplanned distribution.
A hypothetical, with the ratio worked out. Marisol dies owning a farming operation together with other property. Her gross estate is $28,000,000, of which the closely held business interest is $13,500,000. Deductions allowable under sections 2053 and 2054, meaning debts, funeral and administration expenses and losses, come to $1,000,000, so the adjusted gross estate is $27,000,000.
The threshold test: 35 percent of $27,000,000 is $9,450,000. The business interest of $13,500,000 exceeds that, so section 6166 is available.
The cap on what may be deferred: the business is $13,500,000 of a $27,000,000 adjusted gross estate, a ratio of 50 percent. Assume for the illustration that the federal estate tax finally due after all credits is $4,000,000; the real figure depends on the exclusion in force and on lifetime gifting, and it is not the point here. Half of that, $2,000,000, may be paid in installments. The other $2,000,000 is due nine months after the death, like any other estate tax.
Spread over the maximum 10 installments, the deferred half is $200,000 a year, with the first payment able to fall as late as 5 years after the normal due date. Interest is charged on the deferred tax throughout.
Now add section 303. If the business is a corporation, all of whose stock in the gross estate is that same $13,500,000, it clears the section 303 threshold as well, because $13,500,000 exceeds 35 percent of $27,000,000. With death taxes of $4,000,000 and section 2053 funeral and administration expenses of $400,000, the corporation may redeem up to $4,400,000 of its own stock from the estate with exchange treatment rather than dividend treatment. And because section 6166(g)(1)(B) carves a section 303 redemption out of the 50 percent acceleration test, doing so does not, by itself, collapse the installment plan. That carve-out is conditional: an amount of estate tax at least equal to the money and property distributed in the redemption has to be paid by the date (g)(1)(B) sets.