The overnight rate is the interest rate commercial banks charge one another to borrow unsecured funds for a single business day. It matters because it anchors the short end of the yield curve, influences broader credit conditions, and serves as the primary operational target through which central banks conduct monetary policy.
How it works
At the end of each business day, commercial banks must balance their cash books and meet statutory liquidity mandates. Some institutions process more customer withdrawals than incoming deposits, leaving a cash shortfall. Other institutions receive a surplus of deposits. Banks resolve these imbalances by lending cash to one another through the interbank money market.
These transactions have an ultra-short maturity of one business day, meaning the borrower returns the principal plus interest the following morning. Central banks set target bands or corridors around this benchmark by offering their own deposit and emergency lending facilities. The market rate trades continuously between these floor and ceiling barriers set by the monetary authority.
When an entire banking system faces an aggregate cash deficit, the central bank injects liquidity through open market operations. Conversely, when surplus liquidity pushes interbank rates below target levels, the central bank absorbs excess reserves through reverse repurchase agreements. Through these daily balancing mechanisms, monetary officials align the actual market rate with their stated policy goals.
Where it shows up in markets
In foreign exchange trading, the overnight rate dictates the daily rollover cost, known as the swap rate or tom-next rate. When traders hold a currency pair past the settlement hour, brokers debit or credit financing interest based on the relative gap between the overnight rates of the two respective national currencies.
Bond markets use the rate as the foundational anchor for short-term sovereign debt, commercial paper, and floating-rate loans. When traders expect an economic shock or policy pivot, trading volumes in overnight index swaps surge. These derivative contracts allow institutional participants to exchange a floating overnight rate for a fixed rate over longer horizons.
Major global financial centres rely on formal overnight benchmark rates to calibrate everyday financial contracts. The Federal Reserve in the United States monitors the Effective Federal Funds Rate. The Eurozone tracks the Euro Short-Term Rate, while the United Kingdom relies on the Sterling Overnight Index Average to price commercial debt obligations.
A concrete example
Consider Bank Alpha and Bank Beta operating within the same currency union. On a Friday evening, Bank Alpha experiences heavy customer withdrawals that total $100,000, leaving its reserve account balance below regulatory requirements. Meanwhile, Bank Beta receives identical deposit inflows from payroll disbursements, producing a matching surplus of reserves that earns zero return.
Bank Alpha borrows $100,000 directly from Bank Beta via an unsecured transaction at the prevailing overnight rate, with repayment scheduled for Monday morning. Bank Alpha avoids penalty fees from the central bank, while Bank Beta earns interest income on previously idle cash. Both institutions begin the next business week fully compliant with local reserve standards.
If the central bank raises its primary target rate, Bank Beta demands a higher annualized rate to part with its reserve cash. Bank Alpha absorbs this increased cost and adjusts the interest terms offered to retail and corporate borrowers. Through this daily mechanism, changes in overnight rates pass directly into the wider real economy.
For the current rate and data: BIS policy rate statistics
Related terms: Policy Rate · Central Bank · Monetary Policy
