How many of a team of 11 can be on leave at the same time?

Two, on the assumption that nine people have to be on shift. The third concurrent absence drops the team below its minimum, and the model expects that to happen on about 40.1 of the 261 working days in a year.

Would a twelfth person fix it?

Mostly, yes. A team of twelve carries headroom of three against the same minimum of nine, so expected short days fall from about 40.1 to about 14.3, roughly 25.8 fewer a year. The only lever at this size that moves the number further is the minimum itself, and dropping it from nine to eight gets to about 10.6.

Are these figures the real risk or the best case?

The best case. The model assumes each of the eleven decides on leave independently of the others, so about 40.1 short days a year is a floor. Real leave clusters, and at a peak absence rate the team averages 2.23 people away against headroom of two, which works out at about 101.9 short days a year if that rate held.

How Many of 11 Staff Can Be Off at Once?

Two of eleven can be away at once, and eleven sits at the worst end of its headroom band: the model expects about 40.1 short days a year.

Can be away at once2

Short days a year40.1

Two. With a minimum of nine on shift, a team of eleven can have two people away and still run, and the model expects it to fall below nine on about 40.1 of the 261 working days in a year. That is more short days than any smaller team carrying the same headroom, and more than every larger team in this library.

How often that many are actually away

The average is 1.39 people away, and averages do not break rosters. What breaks a roster is the tail: the days when more people than usual are off at the same time. With 11 people each away on 12.6 percent of working days, this is how a year of 261 days is expected to distribute.

0 away

59 days

1 away

93.9 days

2 away

68 days

3 away

29.5 daysshort

4 away

8.5 daysshort

5 away

1.7 daysshort

6 away

0.3 daysshort

7 away

0 daysshort

Everything below 3 away fits inside the roster. Everything from 3 up is a day the operation runs under its minimum of 9, and those add up to about 40.1 days a year.

What is hard about 11

Headroom does not grow smoothly with the team. It moves only when the team crosses a whole-person boundary, so expected short days saw-tooth rather than fall. Teams of eight, nine, ten, and eleven all carry the same headroom of two, and across that run the expected short days climb steadily: about 18.1 a year at eight, 24.7 at nine, 32 at ten, and 40.1 at eleven. Eleven is the end of that run. It is the largest team still sharing only two absence slots, and it pays the most for them, because each of the eleven brings a 12.6 percent chance of being away on any working day and none of them brings extra tolerance.

That makes the twelfth person unusually valuable here, and not for the reason usually given. A team of twelve carries headroom of three, which against the same floor of nine on shift means the twelfth hire is pure tolerance: the minimum does not move, the cover does. Expected short days go from about 40.1 to about 14.3, a difference of roughly 25.8 days a year for one head. Put the other way round, an eleven-person operation is short more often than every team in this library except a six, at 44.3 days, and a seven, at 57, both of which are running on a single person of headroom.

The peak column is where this size stops being an argument about rounding. On an average working day 1.39 of eleven are away, comfortably inside the headroom of two. In a peak leave period the figure is 2.23, which is already past it, so the average peak day is a short day rather than an unlucky one, and that rate across a year works out at about 101.9 short days. The model also treats each person's absence as independent of everyone else's, which is the assumption most generous to the roster. Real leave clusters on school holidays and the last two weeks of December, so 40.1 is a floor on the risk rather than a forecast of it. The 275 person-days of leave the team owes each year have to land somewhere, and they will not land evenly.

Move the minimum, move the answer

The team size is usually fixed. The minimum on shift often is not, and it is the faster lever: making one role coverable for a day changes the arithmetic more than a hire does.

Minimum on shift	Can be away	Short days a year
10	1	108.1
9assumed	2	40.1
8	3	10.6
7	4	2
6	5	0.3
5	6	0

What this assumes, and where it is generous

These figures treat each person as independently likely to be away, which is the assumption most favourable to the roster. Real leave clusters: school holidays, the last fortnight of December, and the local summer shutdown pull requests onto the same dates. Treat every number here as the best case, and the peak column as a reminder of how far the real case sits from it.

Run the same team at a peak concentration of 1.6 times the ordinary rate, which is a stated planning assumption rather than a measured figure, and the expected count away rises from 1.39 to 2.23. Held across a full year, that rate would imply about 101.9 short days rather than 40.1. Real years are neither, but the gap between the two is the size of the scheduling problem that leave clustering creates.

The inputs are 25 days of paid annual leave and 8 days of average sickness per person. Both vary by country, and the relief factor library carries sourced figures for 17 of them, from zero statutory leave in the United States to 28 days in the United Kingdom. Swap your own numbers in and the shape of the distribution holds even as the counts move.

What to do with this

Treat two concurrent absences as the hard ceiling and move the third request to a different week, because the model already expects the floor of nine to break on about 40.1 days a year without anyone stacking requests.
Price the minimum before you price the hire: taking the minimum on shift from nine to eight cuts expected short days from about 40.1 to about 10.6, while pushing it up to ten raises them to about 108.1.
Ration peak weeks under a separate rule from the rest of the year, since a peak absence rate puts 2.23 people away on the average day against headroom of two and implies about 101.9 short days at that rate.

Common questions

How many of a team of 11 can be on leave at the same time?: Two, on the assumption that nine people have to be on shift. The third concurrent absence drops the team below its minimum, and the model expects that to happen on about 40.1 of the 261 working days in a year.
Would a twelfth person fix it?: Mostly, yes. A team of twelve carries headroom of three against the same minimum of nine, so expected short days fall from about 40.1 to about 14.3, roughly 25.8 fewer a year. The only lever at this size that moves the number further is the minimum itself, and dropping it from nine to eight gets to about 10.6.
Are these figures the real risk or the best case?: The best case. The model assumes each of the eleven decides on leave independently of the others, so about 40.1 short days a year is a floor. Real leave clusters, and at a peak absence rate the team averages 2.23 people away against headroom of two, which works out at about 101.9 short days a year if that rate held.