Quantitative Easing and Central Bank Balance Sheets
When policy rates hit zero, a central bank can still act by buying long-term bonds outright — expanding its own balance sheet to push down yields the rate lever can no longer reach.
Prerequisites: Money Supply and the Money Multiplier
A central bank's usual lever is the short-term policy rate. But that lever has a floor near zero, and once it's there, cutting further stops being an option — yet the economy might still need more support. Quantitative easing (QE) is what a central bank does instead: it buys long-term government bonds and other assets directly, in large volume, paying for them by crediting bank reserves. The point isn't the short rate anymore — it's pushing down yields further out the curve that the policy rate never directly touched.
QE works by making the central bank's balance sheet bigger, not by cutting rates further. Large-scale bond purchases push bond prices up and yields down, push investors into riskier assets in search of return, and add reserves to the banking system — a different transmission channel than conventional rate cuts.
What actually happens on the balance sheet
Every asset the central bank buys appears on one side of its balance sheet; every dollar it pays for them appears as a liability — specifically, as reserves credited to the seller's bank. The balance sheet grows on both sides simultaneously:
In words: the central bank isn't printing cash and handing it to people — it's swapping one financial asset (a bond, held by some investor) for another (a reserve balance, held by a bank), and that swap changes the composition of what the private sector holds without directly changing anyone's net wealth. Because there are now more bonds off the market and more reserves sitting in the banking system, the price of the remaining bonds tends to rise and their yield falls, and some of that reserve money looks for a home in riskier assets.
Worked example
A central bank announces it will buy $600bn of government bonds over six months. Before the program, its balance sheet holds $2 trillion in bonds and $2 trillion in reserve liabilities. After the purchases: $2.6 trillion in bonds, $2.6 trillion in reserves — a 30% expansion of the balance sheet. If those purchases are concentrated in 10-year bonds and pull the 10-year yield down from 3.5% to 3.1%, a corporate that would otherwise borrow at a spread over that benchmark now finances more cheaply too, which is exactly the transmission channel QE is meant to open once the policy rate itself has nothing left to give.
What this means in practice
QE reshapes term premia and pushes investors down the risk spectrum — pension funds and insurers that need yield often can't get enough of it from now-lower government bond yields and rotate into corporate credit or equities instead, a channel called portfolio rebalancing. Traders watch the pace and composition of purchases (which maturities, which asset classes) as closely as the headline size, because that's what tells you which part of the yield curve or which market is getting the direct support.
QE does not "print money" in the sense of directly handing consumers cash — it swaps bonds for bank reserves, a liability that stays within the banking system unless banks choose to lend it out. Whether QE is inflationary depends heavily on that second step actually happening, which is why QE eras have produced very different inflation outcomes depending on the broader environment.
Related concepts
Practice in interviews
Further reading
- Bernanke, 'The Federal Reserve and the Financial Crisis'