In Monopoly, what does the official rule say happens when the bank runs out of money?

When the Monopoly bank runs out of money, the banker issues more money as needed.

The standard rules do not impose a fixed limit on the bank’s cash. If the bank has no bills left, the banker can create additional money by writing on paper or using another agreed substitute. This keeps the game operating and is different from shortages of houses or hotels, which can affect whether players may build.

The banker is a player appointed to manage the bank, but the banker’s personal money must remain separate from the bank’s money. The banker handles property deeds, buildings, taxes, salaries, and loans, while still participating as a player if the group chooses.

A common house rule treats an empty bank as a crisis or distributes a limited cash supply. Neither is the classic official rule. The bank can effectively have unlimited money, although the physical set contains a finite number of printed notes.