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Overnight Rate: Key Interest Rate for Interbank Lending

Fixed Income

A comprehensive overview of the Overnight Rate, the interest rate at which major banks lend to one another on the overnight market, along with key indexes like SONIA and EONIA.

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The Overnight Rate is the interest rate at which major banks lend to one another on the overnight market, meaning for repayment the next day. This rate plays a crucial role in the financial system as it influences other interest rates and is often used as a benchmark for various financial instruments.

Key Indexes

Several key indexes track the average overnight rate, providing important benchmarks:

  • SONIA (Sterling Overnight Index Average): This is an important interest rate benchmark for the British Pound.
  • EONIA (Euro Overnight Index Average): This served as a reference for the Euro, though it has largely been replaced by the €STR (Euro Short-Term Rate).

Mathematical Model

The overnight rate can be described using the following formula:

$$ R = \frac{I}{P} \times \frac{360}{d} $$
Where:

  • \( R \) is the overnight rate
  • \( I \) is the interest paid
  • \( P \) is the principal amount
  • \( d \) is the actual number of days in the loan period (usually one day)

Importance

The overnight rate is crucial for:

  • Monetary Policy: Central banks adjust the overnight rate to control inflation and manage economic growth.
  • Liquidity Management: Banks rely on overnight borrowing to manage liquidity and ensure smooth operations.
  • Benchmarking: Financial instruments, such as loans and mortgages, often use the overnight rate as a reference.
  • Federal Funds Rate: The interest rate at which depository institutions trade federal funds with each other overnight.
  • Repo Rate: The rate at which central banks lend money to commercial banks.
  • Prime Rate: The interest rate that commercial banks charge their most creditworthy customers.

FAQs

Q: Why is the overnight rate important?
A: It is a critical tool for central banks to regulate the economy and influence monetary policy.

Q: How often does the overnight rate change?
A: It can change daily, depending on market conditions and central bank policies.

Q: What are some common benchmarks for the overnight rate?
A: SONIA and EONIA are commonly used benchmarks.

Revised on Monday, May 18, 2026
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