This expression dates back to the early 1800s. Foot can mean the bottom of something, such as the bottom of a mountain. In this idiom, it refers to the bottom of a column of prices on a bill. Originally, footing the bill meant to add up the prices of different items on a bill and find the total cost.

Why is it footing the bill?

The idiom foot the bill is derived from an earlier idiom first used in the 1500s: foot up. This phrase meant to add up the figures on a document and come to a total at the foot of the bill. By the early 1800s, the phrase had morphed into today's form, foot the bill, meaning to pay the total at the foot of the bill.

Can you foot my bill?

COMMON If you foot the bill for something, you pay for it. ... Note: This expression may come from the practice of someone paying a bill and signing it at the bottom, or `foot'.