Money Supply vs Real Money Balances
Money Supply and Real Money Balances are two Money & Monetary Policy concepts in AP Economics that students often mix up. The money supply is the total amount of money circulating in an economy, including cash and checkable deposits. Real money balances (M/P) are the money supply adjusted for the price level, the purchasing power of money rather than its dollar amount. Here is how they compare side by side.
Central banks influence it through open market operations, the reserve requirement, and the discount rate. Common measures are M1 (most liquid) and M2 (broader). Changes in the money supply affect interest rates and aggregate demand.
Dividing the nominal money stock M by the price level P gives the real quantity of goods and services that money can buy. What people actually want to hold is a stable level of real balances, so if prices double, holding the same nominal money halves its real value. This is the variable on the horizontal axis of the money market in many intro and intermediate models.
Money Supply vs Real Money Balances: Dollars vs What They Buy
| Money Supply | Real Money Balances | |
|---|---|---|
| What it measures | The number of dollars in circulation | The purchasing power those dollars command |
| How it is written | M, counted as M1 or M2 | M divided by P, the money supply over the price level |
| Units | Dollars | Baskets of goods |
| Who determines it | The central bank together with the banking system | The central bank and the price level jointly |
| If prices rise with M held fixed | Unchanged | Falls, in proportion to the price rise |
| If M doubles in the long run | Doubles by definition | Returns to where it started once prices adjust |
| Which one affects behaviour | Only through its effect on the other | This one, since it is what money actually buys |
Dividing by the price level is what makes the number mean something
Suppose the money supply is an illustrative $2,000 billion and the price index sits at 100, so the index expressed as a ratio is 1.0. Real money balances are $2,000 billion divided by 1.0, which is $2,000 billion of purchasing power. Now let prices rise by 25 percent, taking the index to 125 and the ratio to 1.25, while the money supply is left alone. Real balances become $2,000 billion divided by 1.25, which is $1,600 billion. Not a dollar left circulation, yet the public can buy 20 percent less with the money it holds, since $1,600 billion is 80 percent of $2,000 billion. To restore the original purchasing power the central bank would have to raise the money supply to 1.25 times $2,000 billion, which is $2,500 billion, because $2,500 billion divided by 1.25 returns $2,000 billion. This is the same distinction as nominal against real anywhere else in macroeconomics. The nominal figure counts units, and the real figure counts what those units command, so only the second one can tell you whether households actually feel richer in cash.
The long run answer is that only the real quantity matters
Because people care about purchasing power rather than the number printed on the notes, they adjust their holdings until real balances match what they want. If the central bank doubles the money supply and nothing real has changed, the extra money is spent, prices are bid up, and the process continues until the price level has roughly doubled too. Real balances end up back where they began, output and employment are unchanged, and the only lasting effect is on the price level. That is /glossary/money-neutrality, and it is the long run half of /glossary/quantity-theory-of-money. The short run is different, which is why the distinction is examinable rather than academic. Prices and wages take time to adjust, so an increase in the money supply first raises real balances, pushes the interest rate down, and stimulates interest sensitive spending. Only later do prices catch up and erase the real gain. The whole disagreement between the short run and long run views of monetary policy can be stated as a question about how quickly P responds to M, and everything else follows from the answer.
Frequently asked questions
What are real money balances?
Real money balances are the money supply divided by the price level, written M over P, which measures how many goods the money in circulation can actually buy. Doubling the number of dollars while prices also double leaves real balances unchanged, since nothing about purchasing power has moved.
Why do economists divide the money supply by the price level?
Because the number of dollars on its own says nothing about what they are worth, and people decide how much money to hold based on what it buys. Dividing by the price level converts a count of currency units into a measure of purchasing power, which is the quantity that actually affects spending decisions.
If the money supply doubles, do real money balances double?
Only in the short run, before prices have adjusted. In the long run the extra money is spent and bids up prices roughly in proportion, so real balances return to their original level and the lasting effect falls entirely on the price level rather than on output.
Live Money Market graph. Drag the curves, or open the full version.
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