SONIA Benchmark

The Bank of England is the administrator for SONIA, the Sterling Overnight Index Average.


The Sterling Overnight Index Average (SONIA) is a widely used interest rate benchmark and the reference rate for sterling Overnight Indexed Swaps (OIS).

SONIA was introduced in March 1997. The Bank of England became its administrator in April 2016, and we introduced a series of reforms of the SONIA benchmark in April 2018 (See Background on SONIA reform section).

SONIA for the previous London business day is published by authorised distributors at 9am. 

Key information for users of SONIA

The SONIA Key features and policies document provides more information on the benchmark, such as the definition, publication arrangements, and short-term contingency arrangements. 

PDFSONIA key features and policies

The Bank has assessed its compliance with the IOSCO principles for Financial Benchmarks.  These principles reflect international best practice for those who run benchmarks. We judge we are compliant with the principles, as summarised in the below figure, and this conclusion has been externally audited.

SONIA Benchmark image
SONIA Benchmark image
SONIA Benchmark image
SONIA Benchmark image


The below diagram illustrates the Bank’s governance arrangements for administering SONIA. 

SONIA Benchmark individual image 5
SONIA Benchmark individual image 6

The SONIA Oversight Committee Terms of Reference and Conflict of Interest Code of Practice are linked below. 

Our administration of the SONIA benchmark and the Oversight Committee’s oversight of it are supported by the SONIA Stakeholder Advisory Group. 

The SONIA Stakeholder Advisory Group Terms of Reference is linked below.


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

To support the transparency of the benchmark determination process, the Bank publishes summary information on errors that did not meet the benchmark republication criteria: 

PDFSummary of impact of data errors

SONIA enquiries, complaints and whistleblowing


For general queries about SONIA, please email


To make a complaint about SONIA, please email


We have established a whistleblowing mechanism to facilitate early awareness of potential misconduct or irregularities relating to SONIA.

Whistleblowing is when an employee reports suspected wrongdoing at work. An employee can report things that are not right, are illegal or if anyone at work is neglecting their duties, including:

  • someone’s health and safety is in danger
  • damage to the environment
  • a criminal offence
  • a person not obeying the law
  • covering up wrongdoing.

Firms are encouraged to consider setting up appropriate internal procedures which will encourage workers with concerns in relation to the SONIA benchmark to blow the whistle.

If your employer does not have an internal whistleblowing procedure, or if you do not feel able to use it, then contact us on +44 (0) 203 461 8703 during office hours. Alternatively, you can email us at or write to us at: IAWB Team, PRA CCS, Bank of England, 20 Moorgate, London EC2R 6DA.

Legal protection of whistleblowers

Under UK whistleblowing legislation, workers who make ‘protected disclosures’ have certain protection against detrimental treatment by their employer. While some types of disclosure to us are automatically protected in this way, disclosures relating to SONIA are not currently automatically protected.

However, a disclosure by a worker to a person other than their employer (such as to the Bank of England) can be a protected disclosure if it is carried out using a procedure which the worker’s employer has authorised the individual to use. If you are intending to make a disclosure to us in relation to SONIA, you should consider reviewing your employer’s whistleblowing procedures or consulting your workplace’s whistleblowing champion (if there is one) to determine whether your employer has authorised disclosure to the Bank of England. 

Whistleblowing to the Financial Conduct Authority (FCA) in relation to misconduct is treated as a protected disclosure. If you would prefer to whistleblow to the FCA, you can call 020 7066 9200 during office hours. Alternatively, you can email or write to: Intelligence Department (ref PIDA), The Financial Conduct Authority, 12 Endeavour Square, London, E20 1JN.

Note that the above is not a comprehensive statement of the law on whistleblowing. If you are in doubt as to your legal position, consider obtaining independent legal advice. Further guidance on whistleblowing is also available from the UK Government.

Background on SONIA reform

We reformed the SONIA benchmark on 23 April 2018. The main changes were:

  • We took over the production of SONIA, including the calculation and publication from the Wholesale Market Brokers Association (WMBA)
  • Inputs to SONIA were broadened to include overnight unsecured transactions negotiated bilaterally as well as those arranged through brokers. These data are collected using our Sterling Money Market data collection
  • The averaging methodology for calculating SONIA changed to a volume-weighted trimmed mean
  • The SONIA rate for a given London business day is now being published at 9am on the following London business day to allow us time to process the larger volume of transactions it will capture. Previously it was 6pm on the same day.

We undertook several rounds of consultation on these reforms. In March 2017 we published a summary of the consultation feedback and design of SONIA.

Illustrations of SONIA characteristics under each methodology can be found below:

PDF Characteristics of SONIA under the reformed and previous methodology

ExcelData presented in the SONIA key features and policies document

This page was last updated 12 February 2019
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