Chicken math gets most of us...
We originally start wanting about 8 - 10. I built a coop large enough to house 20 birds and the run large enough for about 30 birds. We ended up getting 15 the first year.
About Jan of the second my daughters started begging for more chicks. I told them there was only room for about 5 more birds in the coop. They said that was not enough. After they thought about it a couple of days they came back to me and asked if we could move their playhouse next to the run and convert it into a second coop. They did not use it much anyway. It was a huge project to move but I did it. Now we had room for 20 more birds in the new coop!. We got 25 chicks late time (two years ago) after planning to get 20. That put us at 35 birds, which was a few too many for the run. That was enough for awhile. In the last year or so we have given away a couple and lost some.
We are down to only 27 now. Some will be 3 years old and the others 2 years old in the next few weeks. We have noticed a reduction in egg production since last year, especially this last winter when we dropped down to 1 egg per day for awhile. We decided in December that it is time to get some new chicks this spring to start replacing some of the older birds. There were a couple of improvements I wanted to make to my run this winter. While working on the changes I realized with the work I was doing it would be pretty easy to add on another 8' x 16'. I just finished that up a couple of weeks ago. Now I have lots of available room.
Our current plan for this year is to get rid of about 7 older birds (yes this willl really happen.) The rest of the picture is not totally clear yet. We plan to get about 20 chicks between Apr 6 and Apr 13. Of course I have to allow for the possibility of 2 or 3 roosters (which I won't keep). And you know how it is at the feed store, it is often difficult to decide between a couple of birds which one to bring home and so you have to get the both. And then when you are done buying chicks for the year you hear of a nearby feed store that just got in a breed that you really wanted but could not find and they have chicks available...