Why don't anime seasons have a standard amount of episodes? Anime seasons are generally 12/13 episodes long. There are quite a number of exceptions though, where more or fewer episodes are fitted into the same timeslots. Most notably, however, a season can have 11,12 or 13 episodes a season. I've seen this discrepancy occur regularly.

I would have thought that keeping the episode amount standard is good for keeping the seasons aligned &mdash; 52 weeks in a year / 4 seasons in a year = 13 episodes per season. The variant I see most is 12 episodes at a time or 12 episodes with a bonus DVD-only OVA. What do they do with the 1 week gap?

Do stations plan their seasons far enough in advance to make it even out overall? What if a show is cancelled?

Why does this anomaly exist? Surely it makes it awkward to schedule TV.
This seems to happen in most regions. The typical reasons I've seen given are:


shows don't all start on the same day or even the same week
sometimes airtime slots are occupied by sports, seasonal, or other non-regular programs
networks may choose not to broadcast new episodes on holidays with historically low viewership
shows are sometimes only given an awkward number of slots like SuperGirl here.


I would also hope that some studios choose to show more or less episodes to ensure they have the right pacing and tell the whole story without an obnoxious amount of filler.

I imagine networks know pretty far in advance what their lineup will look like. Pilot episodes or other proposal material is submitted to the network far in advance for them to review before agreeing to broadcast. It is also important to remember that a large portion of every day's slots belong to re-runs so cancellations just call for more of those.