Checkable deposits are counted in M1 because they can easily be used as a:

1. What lands a deposit in M1 is how spendable it is. 2. The definition of M1 includes checkable, or demand, deposits. 3. One can easily use those deposits as a medium of exchange. 4. They are used that way to buy goods and services. _Source: OpenStax Principles of Macroeconomics for AP Courses 2e (CC BY 4.0), Ch 13 'Money and Banking'_