The federal government uses a system of accounting known as accrual basis accounting. This means that transactions are recorded when they occur, regardless of when the money is actually exchanged. So, for example, if the government were to purchase a new fleet of vehicles, the cost would be recorded as soon as the contract was signed, even though the vehicles might not be delivered and paid for several months later.
This system provides a more accurate picture of the government's financial position than cash basis accounting, which only records transactions when cash changes hands. However, it can be more complicated to track and report on accrual basis transactions.