"Foot the bill" is informal, but also has the nuance that you are taking responsibility for the bill, despite the fact that there are other people who might also take responsibility for the bill, and usually this is not used in relation to restaurant visits, but rather in paying for a larger item of expense, such as construction works or university tuition fees or compensation for injury. For example, I could go to eat alone at a restaurant and pay the bill, but I would not speak about footing the bill in that situation. Maybe if I go to the restaurant with a group of friends I might speak about offering to foot the bill, meaning that I would pay for everyone. However suppose I own a business and my business partner drives his lorry into someone's house by accident, causing damage which is expensive to repair. Perhaps in order to avoid involving the insurance company, I could offer to foot the bill. Or someone's parents could end up footing the bill for their university education.

The meanings are different. We have an accountant who pays our bills. (He isn’t using his own money. He’s employed by the company to make the actual payment.) I forgot my wallet. Can you pay the bill? I’ll pay you back. (It’s my responsibility to pay, but someone else is going to do it, and be reimbursed later) ‘Footing the bill’ is taking responsibility for certain expenses which might not obviously be yours. It’s figurative- it’s not talking about paying an actual bill. John’s grandfather foot the bill for John’s medical training. (It doesn’t mean the grandfather paid an actual bill. It means he reimbursed all of John’s costs) It’s customary for the bride’s parents to foot the bill for her wedding. (There isn’t just one bill. It means they cover all of the costs.)

Hi Ethan. “Foot the bill” is an informal way of expressing that you will “pay for the bill”. Another informal way is to “pick up the check”. Hope this helps

“Foot the bill” is an informal way.

Hey. To pay the bill is more of a formal way while to foot the bill is informal, but it means the same thing really. If you'd like to practice more and improve your English language I am available for that you can check out my profile for bookings. Cheers