Accounting for bank accounts
Bank statements are accounting records produced by banks under the various accounting standards of the world. Under GAAP and IFRS there are two kinds of accounts: debit and credit. Credit accounts are Revenue, Equity and Liabilities. Debit Accounts are Assets and Expenses. This means you credit a credit account to increase its balance, and you debit a debit account to decrease its balance.
This also means you debit your savings account every time you deposit money into it (and the account is normally in deficit), while you credit your credit card account every time you spend money from it (and the account is normally in credit).
However, if you read your bank statement, it will say the opposite—that you credit your account when you deposit money, and you debit it when you withdraw funds. If you have cash in your account, you have a positive (or credit) balance; if you are overdrawn, you have a negative (or deficit) balance.
The reason for this is that the bank, and not you, has produced the bank statement. Your savings might be your assets, but the bank's liability, so they are credit accounts (which should have a positive balance). Conversely, your loans are your liabilities but the bank's assets, so they are debit accounts (which should also have a positive balance).
Where bank transactions, balances, credits and debits are discussed below, they are done so from the viewpoint of the account holder—which is traditionally what most people are used to seeing.
source : http://en.wikipedia.org/wiki/Bank
