S6166_Paragraph
(b1) - Section 6166(b)(1) - Interest in a Closely Held Business
Section 6166(b)(1)(C)  - Example 4
Decedent owned 19% of the voting stock of Corporation A. There are more than 45 shareholders. The gross value of Decedent's 19% interest is discounted 28% to arrive at its §6166(b)(4) estate tax value, which is more than 35% of the adjusted gross estate. This is the only business interest for which a §6166 election is contemplated. Three of the other shareholders are family members described in §267(c)(4) who own a total of 15% of the voting stock (5% each). Even after their ownership interests are automatically attributed to Decedent under §6166(b)(2)(D), there are still more than 45 shareholders. The estate does not make a §6166(b)(7) election.
Result: The discounted estate tax value of Decedent's 19% portion of the voting stock does not qualify for a §6166 election. It does not meet the 20% test of §6166(b)(1)(C)(i).
Section 6166(b)(1)(C)  - Example 4 
Corporation A - More Than 45 Shareholders
Some Shareholders are §267(c)(4) Family Members
Full value of Corporation A50,000,000.00
Outstanding shares of voting common stock10,000
Per-share value of voting common stock5,000.00
Corporation A Shareholders
Total number of shareholders including Decedent50
Brother - §6166(b)(2)(D) attribution to Decedent1
Sister A - §6166(b)(2)(D) attribution to Decedent1
Sister B - §6166(b)(2)(D) attribution to Decedent1
Number of shareholders after §6166(b)(2)(D) attribution to Decedent47
Corporation Value Included in Decedent's Gross Estate
Per-share value of voting common stock5,000.00
Valuation discounts28%
Discounted estate tax value per share3,600.00
Shares of voting common owned by Decedent at date of death - 19% of the total1,900
§6166(b)(4) estate tax value of Decedent's interest in Corporation A6,840,000.00
§6166(b)(6) Adjusted Gross Estate Computation
Gross estate20,840,000.00
Sections J, K, and L deductions - §2053 and §20545,250,000.00
§6166(b)(6) adjusted gross estate15,590,000.00
§6166(a)(2) Ratio Computation
Section 6166 closely held business amount6,840,000.00
Section 6166(b)(6) adjusted gross estate15,590,000.00
Section 6166(a)(2) ratio - maximum amount of tax which may be paid in installments - Does Not Qualify for a §6166(a) 14-year Extension even though the ratio is greater than 0.350000 - the 20% requirement of §6166(b)(1)(C)(i) is not satisfied.0.438743

There are more than 45 shareholders in Corporation A and the estate tax value of Decedent's interest in Corporation A exceeds 35% of the adjusted gross estate. Less than 20% in value of the voting stock in Corporation A is included in Decedent's gross estate. Three of the other shareholders are family members described in §267(c)(4). After the automatic attributions of §6166(b)(2)(D), there are still more than 45 shareholders. The Decedent's interest in Corporation A does not qualify for a §6166 extension. When there are more than 45 shareholders, §6166(b)(1)(C)(i) requires that Decedent's gross estate must include 20% or more in value of the voting stock in Corporation A.

In this example a §6166(b)(7) election is not made.