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What sits on each side of the ledger, and why it moves

What a central bank owns and what it owes sit on the same statement banks and governments use for their own accounts: assets on one side, liabilities on the other, and the two always match. On the asset side sit the securities a central bank has bought, mostly government bonds. On the liability side sits the money it has created to pay for them, most of which lands in the reserve accounts commercial banks hold at the central bank.

That second part is the one people find odd. A bank does not pay for a bond out of a pot of savings. It credits the seller's bank with reserves, a form of money that only exists as an entry in the central bank's own books, and that entry is new. The bond bought is an asset. The reserves created to buy it are a liability. Both sides grow by the same amount, at the same moment.

Why the size of the balance sheet is watched at all

The total tells you how much of this reserve creation is outstanding at any point, and the direction it is moving tells you whether a central bank is currently adding to the reserves in the banking system or withdrawing them. Neither movement is really about the money itself. It is about the price and quantity of longer-term debt in the market, since buying large quantities of it is what pushes its price up and its yield down, and letting it run off does the reverse.

A bond bought and held is also a bond no longer available for someone else to buy, and a market with fewer bonds in private hands tends to price the remaining ones differently. That is the channel through which balance sheet size is meant to affect longer-term borrowing costs, distinct from the shorter-term policy rate a central bank sets separately.

The mechanism

What actually happens when the Fed buys a bond

A bond purchase does not turn into new money in one leap. It moves through a short chain of accounting entries, each one a specific action taken by a specific institution, and it is worth following that chain step by step.

  1. The Committee directs a purchase

    When the Federal Open Market Committee decides to expand the balance sheet, it directs the Federal Reserve Bank of New York's trading desk to buy Treasury securities or agency mortgage-backed securities in the open market. This is what people mean when they say the Fed is buying bonds: the purchase is one of the open market operations, the Fed's term for buying and selling securities to move money through the banking system.

  2. The trading desk buys from a dealer

    The desk does not buy from members of the public. It deals with a small group of banks and securities firms known as primary dealers, who hold government securities and sell them to the Fed in exchange for payment.

    The dealer is part of a bank

    Payment lands directly in that bank's own reserve account at the Fed.

    The dealer is a separate securities firm

    Payment passes through the dealer's clearing bank, which credits the dealer's account and receives the new reserves on its behalf.

  3. Reserves appear in a bank's account

    Reserves are the deposits banks hold in their own accounts at the Federal Reserve, much as a household holds a deposit at a commercial bank. The Fed pays for the bond not with printed currency but by adding a matching amount to the seller's bank's reserve account, an entry made in the Fed's own books.

    This is the step usually meant by talk of the Fed creating money: the reserves did not exist before the purchase settled, and afterwards they do.

  4. The balance sheet grows on both sides

    The bond the Fed has just bought becomes an asset, something it now owns. The reserves it credited to the bank become a liability, money the Fed now owes to that bank. Both sides grow by the same amount, so the balance sheet expands without the Fed borrowing or spending in the ordinary sense of either word.

The size of a purchase changes the scale of the entries, not their shape: a single bond and a programme running to a much larger total move through the same steps.

What quantitative tightening actually does

Quantitative tightening runs the same machinery in reverse. Under quantitative easing the Federal Reserve buys bonds and pays for them by crediting reserve accounts, so both sides of its balance sheet grow together. Quantitative tightening does not sell those bonds back. It simply stops replacing them.

What happens when a bond matures

Every bond the Federal Reserve holds has a maturity date, the point at which the US Treasury or the agency that issued it repays the face value. Ordinarily the Fed would take that repayment and buy a new bond with it, keeping its holdings level. Under quantitative tightening it lets some or all of that repayment go instead, and the bond simply drops off its books.

Why reserves drain

The money used to buy that original bond came from crediting a bank's reserve account, the balance a bank holds at the Federal Reserve. When the bond matures and is not replaced, that credit is not renewed either, so the reserve balance falls. Multiply that across the portfolio and total reserves in the banking system shrink along with it.

What this does to the balance sheet

Assets and liabilities move together, as they did on the way up. Fewer bonds held means a smaller asset side; fewer reserves credited means a smaller liability side. The balance sheet contracts at the pace bonds happen to mature.

Reading the weekly H.4.1 release

The Federal Reserve publishes its balance sheet every week in a release called the H.4.1, formally titled Factors Affecting Reserve Balances. It comes out on the Federal Reserve Board's own website on a fixed weekly schedule, and it is the primary record of what the Fed holds and what it owes, updated as of the Wednesday of each week.

What the release actually lists

The H.4.1 is laid out the way any balance sheet is: assets on one side, liabilities on the other. On the asset side, the largest lines are usually Treasury securities and mortgage-backed securities, the bonds the Fed has bought over time. On the liability side, the largest line is normally reserve balances, the money that commercial banks hold on deposit at the Fed. A smaller liability line covers currency in circulation, the physical notes held by the public.

Each line carries a value as of the date printed at the top of that week's release, so a figure taken from the H.4.1 is only ever true for that Wednesday and needs to be read alongside the date it was published under.

Reading the change from one week to the next

The release is published as a snapshot, so the way to see a trend is to set two weeks side by side and subtract. A rise in the Treasury securities line, matched by a rise in reserve balances, is the signature of the Fed buying bonds. A fall in both, moving at a steady pace, is the signature of bonds maturing without being replaced. Watching a single week rarely tells you much; watching several weeks in sequence is what shows the direction the balance sheet is moving in.

  • Compare the same lines across two or more weekly releases.
  • Check the date printed on each release, since it applies only to that Wednesday.
  • Look at both sides of the sheet together, since a change on the asset side is normally mirrored on the liability side.

Reading the release this way turns a single number into a record you can trace over time, using nothing but the figures the Fed already publishes each week.