Monetary base

The monetary base (M0) is the narrowest monetary aggregate: it consists of (1) physical currency — banknotes and coins in circulation outside the banking system — and (2) commercial bank reserves held at the central bank. These are the direct liabilities of the central bank. Unlike broader money supply measures (M1, M2, M3), the monetary base excludes deposits held by households and firms.

The monetary base is sometimes called "high-powered money" because commercial banks use it as the foundation for creating broader money through lending. Under fractional reserve banking, each unit of central bank reserve can support multiple units of deposits (the money multiplier). In practice, post-2008 QE programmes created enormous reserves that sat at central banks earning interest, weakening the mechanical relationship between the base and broader money growth.

Quantitative easing (QE) directly expands the monetary base. When a central bank purchases government bonds from commercial banks, it pays by crediting those banks' reserve accounts — creating new central bank reserves. The Fed's monetary base grew from roughly $800 billion in 2008 to over $6 trillion at its 2022 peak as a result of three QE rounds. The ECB and Bank of England had similar expansions.

A critical point: large monetary base growth does not automatically cause inflation. The crucial variable is velocity of money — how fast money circulates through the economy. In the 2008–2020 period, QE expanded the base massively but inflation remained low because velocity collapsed: banks held reserves rather than lending them out, and consumers saved rather than spent. The post-2021 inflation surge had different causes (supply shocks, fiscal stimulus) and coincided with broader M2 money supply growth, not just base money growth.

The reverse of QE — quantitative tightening (QT) — reduces the monetary base by allowing maturing bonds to roll off the central bank's balance sheet without reinvestment, or by actively selling bonds. The Fed began QT in June 2022, reducing its balance sheet from $9 trillion to around $7 trillion by late 2026. The ECB's balance sheet declined from €8.8 trillion to €6.4 trillion over the same period.

QT reduces the monetary base but does not directly reduce M2 (broad money) or inflation in a simple mechanical way — the relationship depends on how banks respond. If banks shrink lending as reserves fall, credit contracts and demand cools. Central banks monitor the monetary base alongside broader aggregates, bank lending surveys, and inflation data. The FRED monetary base series (BOGMBASE) is updated weekly for the US.