The monetary base is a monetary aggregate consisting principally of currency in circulation and banks’ reserve balances at the central bank, with precise coverage set by the publishing authority. Also called base money, it measures a different layer of the monetary system from the commercial-bank deposits that households and businesses spend. For a quant, that distinction matters when turning central-bank balance-sheet changes into market signals: a larger base does not mechanically imply a matching increase in bank lending or consumer prices.
Define both sides before adding
A useful two-component representation is
where is the monetary base, is the relevant currency stock and is reserve balances at the central bank. These electronic balances are assets of the account-holding banks and liabilities of the central bank. They are distinct from customer deposits, which are liabilities of commercial banks.
The Federal Reserve’s H.6 definitions, checked for the 27 October 2026 release, make the US boundary explicit:
- Base currency includes Federal Reserve notes and coin outside the US Treasury and Federal Reserve Banks, including cash in depository institutions’ vaults.
- Reserve balances are depository institutions’ balances in master accounts and excess balance accounts at Federal Reserve Banks.
- The monetary base is the sum of those components. Treasury deposits at the Fed are not an additional base component.
Count vault cash once. A textbook may instead write currency held by the public plus bank reserves including vault cash. That can describe the same total with a different partition. Adding currency that already includes vault cash to a reserves measure that includes it again overstates the base. Historical series need particular care: H.6 says its total-reserves measure includes qualifying vault cash before April 2020; reserve balances and total reserves are different concepts.
Coverage also differs internationally. The RBA’s 2018 explanation, Table 1 and footnote 17, includes private-sector notes and coins, banks’ RBA deposits and certain other private-sector RBA liabilities; coins are included even though they are not RBA liabilities. The ECB explains that banks may hold funds in current accounts or the deposit facility. A minimum-reserve requirement is therefore not the same object as all balances held at a central bank. Read the chosen series definition rather than imposing one country’s account labels on another.
A reserve addition changes the total
Consider a fictional economy, in millions of currency units. For this example only, means issued banknotes outside the central bank, including notes held by the public and in bank vaults. means banks’ account balances at that central bank. There are no coins or other base components.
| Component | Before | Change | After |
|---|---|---|---|
| Issued notes outside the central bank | 60 | 0 | 60 |
| Reserve balances | 40 | +10 | 50 |
| Monetary base | 100 | +10 | 110 |
The central bank buys securities from a commercial bank’s own portfolio and credits its reserve account by 10. With no other transactions, currency is unchanged and
The base grows by . This is an accounting result under the stated boundary, not an observed national statistic.
Original fictional example, in millions of currency units. Currency includes issued notes in public hands and bank vaults; reserve balances exclude vault cash.
The selling bank swaps securities for reserves. Its customers’ deposits do not rise in this transaction. A purchase from a nonbank seller paid through a bank would require an additional customer-deposit entry; the central-bank article follows that distinction through the balance sheets. Quantitative easing can expand reserves through asset purchases, but the base alone does not identify the transaction’s purpose or counterparty.
An aggregate is not a lending rule
The money supply includes measures of money held by the public, with broader aggregates containing commercial-bank deposits and other eligible instruments. Bank reserves are used for settlement between banks; they are not household spending balances. The Bank of England’s money-creation explanation distinguishes reserves from deposits and explains how lending can create a matching deposit, subject to constraints.
Consequently, neither a fixed deposit multiplier nor a fixed response of lending or inflation follows from the identity . Banks’ capital, funding, credit risk and borrowers’ demand matter. The monetary base is also not the sum of every central-bank liability: use the aggregate’s inclusion rules. For monetary policy, interpret its composition alongside the operating framework and the policy rate.
When using an official series, preserve its currency units, frequency, averaging convention and seasonal-adjustment status. For example, FRED’s BOGMBASE series is monthly, in billions of US dollars, and not seasonally adjusted. Align the observation period and available release vintage before comparing it with a different series or using it in a historical trading model.
Practice: more notes, same base?
In a separate fictional economy using the same two-component convention, issued notes outside the central bank are 25 and reserve balances are 75, both in millions. A bank obtains 8 of newly issued notes for its vault by exchanging 8 of its reserve balance. Nothing else changes. Does the monetary base increase?
Answer. No. Notes become and reserve balances become . The base stays at , equal to the original . This changes the composition of base money. Adding the new vault notes without subtracting the reserves exchanged would count a conversion as fresh base creation.
Sources
- Federal Reserve: H.6 Money Stock Measures, Table 1 and footnotes 1–6
- FRED: Monetary Base: Total, BOGMBASE, series definition and units
- RBA: Money in the Australian Economy, Measures of Money, Table 1 and footnote 17 (2018)
- ECB: What are minimum reserve requirements?
- Bank of England: How is money created?