SONIA interest rate benchmark

The Bank of England runs SONIA – the risk-free rate for sterling markets.


SONIA (Sterling Overnight Index Average) is an important

We are the administrator for SONIA. That means we take responsibility for its governance and publication every London business day.

SONIA is based on actual transactions and reflects the average of the interest rates that banks pay to borrow sterling overnight from other financial institutions. 

Financial businesses and institutions use SONIA in a variety of ways. For example, to calculate the interest paid on transactions and sterling  . SONIA is used to value around £30 trillion of assets each year. 

SONIA is the Working Group on Sterling Risk Free Reference Rates’ preferred benchmark for the transition to sterling risk-free rates from Libor.

Our Monetary Policy Committee decides what monetary policy action we take as a central bank. We implement our monetary policy by taking an active role in the financial markets using our Sterling Monetary Framework. SONIA has an important role in measuring how effective that implementation is.     

SONIA was introduced in March 1997. We took responsibility for it in 2016 and, after consultation, we reformed it in 2018. The way we run SONIA complies with international best practice for financial benchmarks.  


Supporting Risk-Free Rate transition through the provision of compounded SONIA

The Bank is seeking views from sterling market participants on two proposals.

How we produce the SONIA benchmark

We gather data

Banks send us details of all their transactions from the previous day by 7am.
Tick with file

We check the data is right

We check the data is in the right format and run plausibility checks to make sure the data we have makes sense.

We calculate SONIA

We calculate SONIA and other statistics we need.

We publish it

For more information, see our overview of how we run SONIA.

If you have any queries about SONIA, please email

Historical data 

SONIA is freely available on our Interactive Statistical Database by 10am on the business day after it is first published. The database also includes historic data. 

To support transparency of the benchmark calculation process, we publish summary information on errors that did not meet our republication criteria. 

This page was last updated 26 February 2020
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