The Big Bang Theory cast's contracts are up at the end of this season, the series' 10th. CBS and Warner Bros., the studio that makes the show, of course want to keep the most popular comedy on TV going indefinitely. But the show is extremely expensive to make, and the cost is only going to go up. And for the actors, 10 years is a long time to stay with a single show and they may be getting bored or restless, no matter how rich it's made them. They may be itching to free up time to work on other projects. So, realistically, how much longer will The Big Bang Theory last?

The good news for fans: Season 10 probably won't be the end.

"We are very confident that everyone involved wants more Big Bang past year 10," CBS president Glenn Geller said at the Television Critics' Association fall preview this summer. "I know Warner Bros will make those deals."

12 TV friendships we're grateful for

Jim Parsons, the highest-paid and most publicly popular member of the cast, says the actors are onboard. He told TVLine in March, "If the opportunity to go past Season 10 came up, I'd be very hard-pressed to tell you who [among the cast] might say no — if anybody would. I wouldn't."

And the off-camera talent is willing to come back, too, with showrunner Steven Molaro saying, "If everything keeps going the way it's been going, absolutely [I'm up for more]."

Contract negotiations are likely to be less heated than they were the last time the cast re-upped in 2014. After Season 7, the three primary cast members — Parsons, Johnny Galecki and Kaley Cuoco — upped their salary to $1 million an episode over three seasons; each member of the trio will earn around $90 million over the life of the deal.

Jim Parsons, Kaley Cuoco and Johnny Galecki, <em>The Big Bang Theory</em>Jim Parsons, Kaley Cuoco and Johnny Galecki, The Big Bang Theory

The really hard part of the 2014 negotiations, however, was between the studio and Simon Helberg and Kunal Nayyar, who were seeking parity with the higher-paid trio on the basis that Howard and Raj had become just as integral to the show as the Leonard-Penny-Sheldon core. The producers were prepared to write Howard and Raj off the show, but a deal was reached that secured the actors about 75% of what Parsons, Galecki and Cuoco make. Each season after that their compensation has climbed, and now all five actors are making around $1 million per episode. Additionally, all five actors get the same percentage of the show's back-end profit. Now that they're all compensated what they feel they're worth, negotiations shouldn't be so tense this time around.

The show has made all five actors mind-bogglingly wealthy — they're the highest-paid actors on television, according to Forbes. Jim Parsons made $25.5 million between June 1, 2015 and June 1, 2016. Cuoco earned $24.5 million over same time period; Galecki made $24 million; Helberg made $22.5 million and Nayyar made $22 million. They don't need to keep making Big Bang money to be set, but they certainly don't want to stop making Big Bang money.

The best TV shows of 2016

The show has made them very, very rich. There's no doubt about that. The question is how tired of the show they are. Boredom, more than the money, will be the actors' determining factor in whether they want to keep the show going.

After 13 years of playing the same characters, they'd surely be looking to try something new creatively — or explore new revenue streams. Some of them are already doing it: Simon Helberg has a prominent supporting role in Florence Foster Jenkins, an Oscar contender starring Meryl Streep. Jim Parsons is producing more stuff, like hospital comedy Lakeside VA and the planned Sheldon spin-off, as well as a movie based on a BuzzFeed article in which he will also star. It wouldn't be surprising if they all start using their money to executive-produce stuff, which will allow an even greater share of profits if their projects are successful.

Kunal Nayyar and Simon Helberg, <em>The Big Bang Theory</em>Kunal Nayyar and Simon Helberg, The Big Bang Theory

On the other side of the table, it has to be acknowledged that The Big Bang Theory is crazy expensive to make. According to the BBC, it costs CBS $4 million per episode before factoring in the cast's pay. That figure is from 2014, before they negotiated their current contracts. Let's ballpark estimate that that cost has gone up to $5 million, plus another $6.5 million for the cast. That's, conservatively, $11.5 million dollars for 18 and a half minutes of content per week (The average sitcom pilot reportedly costs about $2 million to make).

At the same time that costs have gone up, ad rates have gone down. According to Ad Age, it costs $289,136 for a 30-second spot on The Big Bang Theory in 2016, down 17% from 2015's rate (though it's still the most expensive non-NFL program to advertise on). The show costs more to produce than it earns in ad revenue. Fortunately, the show made "one of the most lucrative TV syndication deals ever" in 2010, so it's going to make billions over the years. But right now, eventually the show is going to become so expensive that it will no longer be worth producing.

The Big Bang Theory may have to figure out a better way to keep cost & cast flexible. Shorter seasons would probably be the best way to keep the show on for a long, long time. Reducing the episode order from 24 to 13 would keep CBS in the Big Bang business while bringing the overall cost down and freeing up the cast to work on other projects.

But more likely, whatever new contract the cast signs will be the last. No one needs to see a 50-year-old Sheldon, especially not when there's a young Sheldon coming down the pike. The money will continue to come in even when they're not making the show anymore, so once they decide they're done, why keep going?