How many episodes in a TV season? Here’s the long and short of it

How long is a TV season? The short answer: The number of episodes varies from one show to another.

The long answer: The traditional U.S. television season for a long time began in September and ended in April. That was later extended into May because networks aired major programs in May to help affiliates whose ratings were measured at the time. Some networks have argued that, instead of a season, ratings should be based on a full year — September to August — because they have summer shows that do well. And many programmers, including cable channels and streaming services, do not feel bound by the seasonal model. More about that in a bit.

Since shows were put in that traditional window, in old TV times a series might make as many as 39 episodes to fill the season, with the other 13 weeks of the year (basically summer) filled by reruns or substitute programming. However, as the cost of making shows and the risk of failure grew, the number of episodes in a season shrank into the mid-20s. That meant more reruns, and broadcast rivals such as cable networks began putting on their new episodes during those broadcast-rerun periods, blunting the audience for the network reruns.

That in turn led to broadcasters moving away from repeats in many cases, and instead airing short runs of new series, whether inexpensive programming such as reality shows or a handful of episodes of a show that might be a contender for the next full season. So, because they were filling gaps, replacement shows’ seasons would be 13 episodes or far less.

But wait, there’s more.

Now we have shows that follow a British model of making only as many episodes as they have enough story, energy or money for. A “Downton Abbey,” for example, never did more than 10 episodes in a season. Benedict Cumberbatch’s “Sherlock” seasons have had three telecasts each, leaving Cumberbatch plenty of time for the big-screen side of his career. When major American actors have come to TV, they often keep their schedules tight (and the producers can have more control of costs). “True Detective” snagged Woody Harrelson and Matthew McConaughey for a season in part by keeping it to eight episodes.

So, as you can see, shows vary in their length. And is that a good thing? Well, for the creators and stars of shows, it can be if a shorter run keeps their creative energies going. A producer once said that, in a 20-plus episode series season, a third would be good, a third so-so and a third bad. It’s possible that shorter, more creatively focused runs reduce the odds of bad episodes — though we can all think of even short-run shows that defy that logic.

And for viewers who simply want to keep track of their favorite shows, this can be a mess. You watch four episodes, and your show disappears for a year or more. Or you’re caught up in a serialized drama when suddenly there’s a “midseason finale” or a “winter finale” followed by weeks and weeks of hiatus or a replacement show you don’t like as much — and then you miss when the show finally returns. You accordingly have to be ever more vigilant with your TV listings and information.