The Big Bang Theory has depicted the lives of a group of friends for over a decade. The ups and downs of their careers, their romantic choices, their familial issues, and of course their conflicts and resolutions amongst the group, have all been displayed on screen.
Money plays a huge part in the show. Indeed, the economics of The Big Bang Theory can be felt in almost every episode. It has come to define the characters in some way, whether it's how they interact with their work, where they live, what they wear or even what they buy. Each character's relationship with money is totally unique and a nuance of the show that shouldn't be overlooked; the economics don't always add up though.
University Funding
In the show, at least, CalTech seems to be pretty inconsistent when it comes to funding projects. In fact, there have been multiple sub-plots throughout the show regarding gaining tenure, getting key research grants, and other such financial benefits from the University.
None of these ever seem to pan out long-term though. It seems that Leonard is eventually granted opportunities on a number of occasions yet is always looking for more. The way money is distributed and spent by the University doesn't make a lot of sense; especially in regards to some of the breakthroughs (or rather lack thereof) the group are having in their respective fields. Of course, some professionals working in academia may argue that this may not make sense, but it's how the real world works!
Penny's Early Financial Issues
Early into The Big Bang Theory Penny is having severe financial issues. She's in debt and even has to borrow money from Sheldon. But her situation thereafter is wildly inconsistent. Penny somehow affords acting classes and has a terrible trait of constant, unnecessary shopping.
She even has to spend money on headshots and travel to and from auditions; all requirements of an actor's life. Yet she somehow also affords her apartment in a building where Sheldon and Leonard have to split the rent on their own place. Surely the Cheesecake Factory doesn't pay that much? Needless to say, her economics only make sense once she has started on a new career path.
The Comic Book Shop's Survival
The comic book shop is one of the key hangout spots in the series. Owned by Stuart, no one ever really seems to be buying anything from the store. Leonard and co seem to browse through the comics mostly and the shop is usually low on customers.
Every now and then the debt of the shop is brought up, although this is then forgotten about again. The shop survives far longer than it should, until an insurance pay-out allows Stuart to remodel and seemingly survive for a few more years.
Affording The Hobby
There are some incredibly nerdy moments throughout the show and it's often a celebrated fact that geek and pop culture is front and center in The Big Bang Theory. But at some stage someone has to ask, how do they afford it all?
Howard living with his mother helps, and Raj's rich family also plays a role, but the amount of collectibles, cosplays, and comic books they all own, linked to the many trips they make to fan events, should surely be pushing Leonard and Sheldon at least into debt.
Raj's Riches
Raj's family are well documented as extremely wealthy. He lives off of this for quite some time, happy to take handouts. He still has a paying job, though, and it's unclear exactly what all these extra riches actually pay for, apart from his hobbies - and his apartment, of course.
When Raj gives up all the money, the only thing that changes is his living location. At one stage he takes on an extra job lecturing on the solar system at the Planetarium, but besides this he doesn't appear to be struggling financially thereafter. It's a real mystery that he doesn't go into massive debt, given how much of a financial change this would be.
The Price Of The Apartments
Sheldon noted early on in the The Dumpling Paradox that he only had to have a roommate because he couldn't afford the apartment by himself. This is, once again, almost the same apartment that Penny rents by herself across the hall (although hers is a one-bedroom, not a two-bedroom). So how expensive are these apartments?
Of course, the show is set in Pasadena, California which likely has some expensive properties. This would explain why Raj needed his riches, but once again raises questions on how he could afford even a smaller place after this. Needless to say, the economics of renting don't totally make sense in the show.
Sheldon's Money Handling
Sheldon has a very strange relationship with money. In The Financial Permeability he claims that he only uses 46.9% of his post tax income, meaning he is incredibly frugal with his finances. Despite having this much available of his salary though, it's strange he has to have a roommate at all.
Of course, he is portrayed often as being very protective of his dollars, but is also happy to give away his money to Penny when she is in need and has very little idea how much to pay for Amy's gift, giving over thousands. There are therefore a number of inconsistencies with his characterization.
Takeout Costs
The group are constantly getting takeout. If they aren't ordering in then they are eating out. This is a lifestyle that Penny can't really afford as Sheldon seems to only want to get food from the best takeout places in the area.
She continues to mooch off of the group though, which Sheldon doesn't seem too troubled by despite his frugality and obsession with how much he's spending. It is of course possible that Leonard could be footing the bill for her, as he has spent a lot of money on Penny already, even buying her a car; one that she eventually sells and tries to pay Leonard back for as their own pay gap starts to shift.
Howard And Bernadette's Pay Gap
There was a particularly notable plot thread that saw Bernadette earn considerably more than Howard; something he had quite a complex about. This was eventually forgotten about, although it does raise a number of questions about Howard's wages.
Controversies about who controls the bank balance asides, Howard is a man who actually went to space and is at the top of his industry. He has flying high in his career and even inherits a house for his family to live in, cutting costs. It's unclear how the pay gap ends up being so large, besides the fact that there's big business in pharmaceuticals.
Nobel Prize Winnings
One of the most well-earned story arcs for Sheldon was when he finally realized his boyhood dream. With the brilliance of his wife Amy, the couple managed to make a breakthrough discovery that won them a Nobel Prize for their work.
The Nobel Prize comes with a huge amount of cash winnings. It's never revealed what Sheldon and Amy were going to do with that money though. The final shot sees the group eating takeout once again in Leonard's apartment. The changing financial situation of the couple isn't really brought up, but is surely a huge factor of the win that will change their life forever.