"The money supply" is one of those phrases that sounds precise but rarely gets explained. How much money is there, really? The answer is not a single number, because "money" is not a single thing, and the measures economists use, with names like M1 and M2, are simply attempts to draw a line around what counts. This explainer follows the Federal Reserve's own description.

What "money" even means here

Start with the definition. The Federal Reserve describes the money supply as "the total amount of money, cash, coins, and balances in bank accounts, in circulation." More broadly, it covers "safe assets that households and businesses can use to make payments or to hold as short-term investments."

That second clause is the key to why there is more than one measure. Some money is instantly spendable, the cash in your wallet, the balance in your checking account. Some is almost-but-not-quite money, sitting in a savings account you would have to move first. Both are "money" in a meaningful sense, but they are not equally liquid, so economists count them in tiers.

M1: the most spendable money

M1 is the narrow measure, the money you can spend right now. The Fed says M1 includes "currency held by the public and transaction deposits" at banks, meaning checking accounts and "other very liquid deposits."

Think of M1 as the money that is already in a form you can use to pay for something today, without converting anything. It is cash in circulation plus the balances you can draw on immediately.

M2: M1 plus the near-money

M2 is the broader, more commonly cited measure. It contains everything in M1 and then adds the next layer out: money that is not quite as liquid but is easily turned into spendable cash.

Specifically, the Fed says M2 comprises M1 plus "small-denomination time deposits (those issued in amounts of less than $100,000) and retail money market mutual fund shares." In plainer terms, that means savings deposits, smaller certificates of deposit, and retail money-market funds, the money households hold as short-term savings rather than for immediate spending. Because it captures both spending money and this near-money, M2 is often treated as the best single gauge of how much money is sloshing around the economy.

Why anyone watches it

The reason these aggregates matter is their historical relationship to the real economy. The Fed notes that money-supply measures have shown "close relationships with important economic variables such as nominal gross domestic product and the price level."

That link is the intuition behind a very old idea: if the amount of money grows much faster than the amount of goods and services, you tend to get inflation, more money chasing the same stuff. A sharp expansion or contraction in M2 can therefore be a signal about where growth and prices may be heading. It is one of the oldest lenses in economics for thinking about inflation.

The important caveat

That said, the money supply is not the master switch it was once thought to be. The Fed is careful to note that while these measures once played a central role, the Federal Open Market Committee now treats money-supply data as just "part of a wide array of financial and economic data that policymakers review" when setting policy.

The relationship between money growth and inflation, once assumed to be tight and mechanical, has proved looser and less reliable in practice, especially as the financial system has evolved. So while a big move in M2 is worth noticing, modern central banks steer using interest rates and a broad dashboard of indicators, not by targeting the money supply directly.

The takeaway

The money supply is the economy's total stock of usable money, measured in widening circles: M1 for what is instantly spendable, M2 for that plus the near-cash households park in savings. The figures matter because, over long stretches, money growth and the size and price level of the economy tend to move together, which makes a rapid change in M2 a classic warning sign for inflation. But it is a gauge to read alongside others, not a lever a central bank pulls on its own. None of this is investment advice; it is simply the vocabulary for one of the most-cited and least-understood numbers in economics.