How many accounts are affected by a transaction?

At least two accounts are affected by a transaction. This is because every transaction involves the transfer of money from one account to another. For example, if you make a purchase at the grocery store, your checking account will be debited and the grocery store's checking account will be credited.

In some cases, more than two accounts may be affected by a transaction. For example, if you write a check to a friend and your friend deposits the check into their savings account, three accounts will be affected: your checking account, your friend's checking account, and your friend's savings account.