Foot the bill

Now means simply to pay the bill with the implication that one is paying for other people as well as oneself. The expression dates from the mid-19th century and makes use of the figurative meaning of foot as the bottom or end, as in the foot of the mountain or ladder. Therefore, the foot of the bill was the total at the bottom. Footing up was also a synonym for adding up that has now largely fallen away but was commonly used in the 19th century. Naturally, anyone would foot up or check the arithmetic before paying a bill.