To calculate a two-thirds majority vote, divide the applicable number of voters by three, multiply the result by two, and round any fraction up to the next whole number. That final figure is the minimum number of “yes” votes the motion needs to pass. The arithmetic is simple; the trap is the word “applicable,” because bylaws define the denominator three different ways, and picking the wrong one is where most miscounts happen.
The Arithmetic
Take the voter count, divide by three, multiply by two. For a committee of 15, dividing by three gives five, and multiplying by two gives 10. Ten “yes” votes carry the motion.
Multiplying by the decimal equivalent, 0.6667, produces the same result. Either method works. Pick one and stick with it so nobody questions the arithmetic during a heated vote. Division-then-multiplication tends to be easier to explain out loud at a live meeting, which matters when the room needs to trust the outcome on the spot.
Always Round Fractions Up
When the math doesn’t land on a whole number, round up. A two-thirds requirement means the “yes” votes must reach at least two-thirds, and since no one casts a partial vote, any fraction above a whole number demands one more person in the “yes” column. Robert’s Rules of Order phrases the standard as “at least two thirds,” which leaves no room for rounding down.
This is where the miscounts happen. If 20 people vote, two-thirds works out to 13.33. Thirteen “yes” votes would represent only 65 percent, short of the mark. You need 14. In a body of 50 members, two-thirds equals 33.33, so 34 affirmative votes are required. A chair who rounds down to 33 has approved a motion at 66 percent, mathematically less than the 66.67 percent threshold.
The standard rounding rule from math class, round to the nearest whole number, does not apply. A result of 13.33 would normally round to 13, but parliamentary procedure doesn’t care about “nearest.” It cares about “at least.” Anything below the exact fraction fails.
Quick Reference for Common Group Sizes
Minimum “yes” votes needed at typical voter counts:
- 5 voters: 4 (3.33 rounds up)
- 7 voters: 5 (4.67 rounds up)
- 9 voters: 6 (exactly two-thirds)
- 10 voters: 7 (6.67 rounds up)
- 12 voters: 8 (exactly two-thirds)
- 15 voters: 10 (exactly two-thirds)
- 20 voters: 14 (13.33 rounds up)
- 25 voters: 17 (16.67 rounds up)
- 50 voters: 34 (33.33 rounds up)
- 100 voters: 67 (66.67 rounds up)
When the voter count divides cleanly by three, no rounding is needed. Every other case rounds up.
Which Number Goes in the Denominator
The arithmetic is the easy part. The harder question is which number you’re dividing. Bylaws, charters, or an adopted parliamentary authority will specify one of three voting bases, and each produces a different threshold.
Two-Thirds of Those Present and Voting
This is the default under Robert’s Rules of Order when the bylaws simply say “two-thirds vote” without further qualification. The denominator counts only the people who actually cast a “yes” or “no” vote. Anyone sitting in the room without voting is irrelevant. If 30 members attend but only 24 cast votes, the threshold is two-thirds of 24, which is 16.
This base produces the lowest hurdle because it shrinks whenever someone declines to vote. Organizations that want supermajority actions to be relatively achievable tend to use this standard.
Two-Thirds of Members Present
Here the denominator is everyone in the room or connected to a virtual meeting, whether they voted or not. If 30 members are present and five don’t cast a ballot, the threshold remains two-thirds of 30, which rounds up to 20. Those five non-voters make the motion harder to pass because they inflate the denominator without adding “yes” votes.
Two-Thirds of the Entire Membership
This is the highest bar. The denominator is every person on the organization’s roster who is entitled to vote, regardless of attendance. If a board has 100 members and only 75 show up, you still need 67 “yes” votes. Absent members function as dead weight against any motion. Organizations use this standard when they want major decisions to reflect overwhelming support from the full body, not just whoever attended.
Read your governing documents carefully. Some organizations use different bases for different types of action. The difference between “two-thirds vote,” “two-thirds of those present,” and “two-thirds of the entire membership” can swing a close vote by several seats.
How Abstentions Change the Math
An abstention is a refusal to vote. Not a “yes,” not a “no,” just silence. Its mathematical impact depends entirely on which voting base your organization uses.
Under the “present and voting” default, abstentions have no effect. The denominator counts only people who actually voted, so abstaining removes you from the calculation. If 24 people vote out of 30 present and six abstain, you need two-thirds of 24, not two-thirds of 30.
Under “members present” or “entire membership” standards, an abstention has the same practical effect as voting “no.” The abstaining member still counts in the denominator, but their silence adds nothing to the numerator. In a room of 30 where six abstain, you still need 20 “yes” votes. Those six abstainers made the threshold harder to reach without actively opposing the motion. This is the single most common reason a motion that “should have passed” doesn’t.
Recusals Work Differently
A recusal happens when a member has a conflict of interest and is disqualified from participating. Unlike an abstention, a recused member typically cannot join discussion or voting, and in many procedural frameworks does not count toward the denominator or even toward quorum. If a nine-member board has one member recuse over a financial conflict, the effective body for that vote shrinks to eight. Two-thirds of eight rounds up to six.
Abstaining members, by contrast, still count toward quorum in virtually every parliamentary system. The distinction matters on a small board where one or two seats swing the math. A formal recusal changes the denominator. A casual “I’ll sit this one out” does not.
What Vacancies Do to the Count
When a seat is empty because of resignation, removal, or death, it generally reduces the total membership count for both quorum and voting purposes. If a board is authorized for nine seats but two are vacant, most parliamentary authorities treat it as a seven-member body. Two-thirds of seven rounds up to five.
The exception is when bylaws define the board as a fixed number of seats rather than a fixed number of members. If the charter says “a board of nine” and a vote requires two-thirds of the board, some organizations interpret that as two-thirds of nine regardless of vacancies, meaning you would still need six votes even though only seven people can cast them. This reading is less common but appears in older corporate charters and some municipal codes. Check the specific language before assuming a vacancy shrinks the denominator.
Quorum Has to Exist First
None of the math matters without a quorum when the vote is called. Quorum is the minimum number of members who must be present before the body can conduct business at all. If the bylaws require a majority of members and only a handful show up, any vote taken, whether simple majority or supermajority, is invalid.
Quorum requirements come from the bylaws. A common default is a majority of the total membership, but organizations frequently set lower thresholds to avoid being paralyzed by poor attendance. Quorum must exist at the time of the vote, not just at the start of the meeting. If members leave early and the room drops below quorum before the supermajority vote is called, the chair cannot proceed.
In organizations that allow proxy voting, proxies typically count toward quorum. A member who submits a proxy is treated as present for both quorum and voting purposes, which can decide whether a meeting can act at all. Whether proxies are permitted depends on the bylaws and applicable state law. Many nonprofit boards prohibit them.
Record the Calculation
Record the calculation method, the specific voting base used, and the exact tally in the meeting minutes. This is the only way to defend the result if someone challenges it later. Minutes should reflect the total number of members present, the number who voted “yes,” the number who voted “no,” the number of abstentions, any recusals, and the mathematical threshold that applied. When the math is transparent and the paperwork is clean, procedural challenges have very little to grab onto.