Key compounds: 账单 (zhàngdān, bill), 账号 (zhànghào, account number), 账户 (zhànghù, bank account), 记账 (jì zhàng, to keep accounts), 算账 (suàn zhàng, to settle accounts - can also mean 'to get even').
history
The 贝 (shell/money) radical shows this character is about finances. Ancient Chinese used shells as currency.
贝 depicts a cowrie shell, ancient Chinese currency. As radical it marks 账 as belonging to the money/wealth family with 财货贵购 - anything dealing with funds, debt, or value owed.
长 supplies the sound (cháng drifted to zhàng) and a faint semantic suggestion of stretching out - fitting for a running tally that grows over time. The same phonetic powers 涨帐胀, all cluster around the zhang reading.
