Bank Book

The term bank book carries two related but distinct senses, and it is worth separating them cleanly. In its older, everyday sense, a bank book — more often called a passbook — is the small booklet a bank once gave a customer to record transactions in a savings or deposit account: deposits, withdrawals, interest, and the running balance, stamped or printed each time the customer visited. It was the customer's own record of the account before online banking made it obsolete. In its modern, technical sense used inside banks, the banking book refers to a category in a bank's own accounting: the portfolio of assets — chiefly loans and securities — that the bank intends to hold to maturity to earn steady interest income, rather than to buy and sell for short-term profit. These two senses share the word 'bank book' but describe very different things. This is educational content, not financial advice.

The distinction matters because the two senses live in different worlds. The passbook sense belongs to retail banking history — a physical ledger for one customer's account, valuable in its day for giving the account holder a tangible record, now largely replaced by statements and apps. The banking-book sense belongs to bank accounting and risk management, where it names one of the two great buckets into which a bank sorts its assets. In that world, whether an asset sits in the banking book or the trading book changes how it is valued, how its risk is measured, and how much capital the bank must hold against it. So when someone says 'bank book,' the intended meaning depends entirely on context: a customer's passbook, or a bank's held-to-maturity portfolio. Most professional finance usage today means the banking book.

Within bank accounting, the banking book is defined largely by contrast with the trading book, and the two are separated by intent. The banking book holds assets the bank means to keep — typically loans it has made and securities it plans to hold to maturity — to earn interest income over time. These assets are generally carried at amortized cost, recognizing interest steadily rather than repricing them daily, which suits their long-term, hold-to-maturity nature. The trading book, by contrast, holds assets the bank intends to actively trade for short-term gain — equities, bonds, currencies, derivatives — and these are marked to market, valued at current prices, because their whole purpose is to be bought and sold.

This split is not a mere labeling exercise; it drives valuation, risk, and regulation. Because banking-book assets are held to maturity and carried at amortized cost, they are chiefly exposed to credit risk (borrowers defaulting) and interest-rate risk over the long term, and they attract capital requirements aimed at those risks. Trading-book assets, marked to market daily, are exposed to market risk — the risk that prices move — and attract capital rules governing that exposure. Regulators care greatly about where an asset sits, because a bank could otherwise game the rules by parking risky trading positions in the banking book to dodge market-risk capital. So the banking-book-versus-trading-book distinction is a load-bearing part of how banks account for assets and how much capital they must hold. It has nothing to do with the retail passbook sense of 'bank book.'

Reading the term correctly means, first, identifying which sense is meant, because the two are so different that mixing them causes real confusion. If the context is a customer's savings account and a physical booklet of transactions, 'bank book' means a passbook — a personal record, now mostly historical. If the context is a bank's balance sheet, accounting, or capital requirements, 'bank book' means the banking book — the held-to-maturity portfolio of loans and securities, defined against the trading book. In professional finance, the banking-book sense dominates, so default to it unless the setting is plainly about a retail passbook. When the banking book is meant, remember the intent-based split from the trading book: hold-to-maturity, amortized cost, credit and rate risk on one side; actively traded, marked to market, market risk on the other. This is general education, not financial advice.

The failures are almost all failures of sense. Reading 'bank book' as a passbook when a bank's held-to-maturity portfolio is meant — or the reverse — produces nonsense. Within the banking-book sense, the common error is blurring it with the trading book, forgetting that intent (hold versus trade) is what separates them and that the separation governs valuation, risk, and capital. Another is assuming the passbook sense is still current when, for most purposes, it is a historical artifact. The discipline is simple: pin down the sense from context, treat the banking book as the live professional meaning, and keep its intent-based contrast with the trading book firmly in mind, because that contrast is where the term does its real work in modern finance.

A bank book means either a customer passbook of transactions or, in bank accounting, the banking book of assets held to maturity, distinct from the marked-to-market trading book.

Etymology: source.

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