SONIA (interest rate)

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SONIA (Sterling Over Night Index Average) is the effective reference for overnight indexed swaps for unsecured transactions in the Sterling market.[1]


It was launched in March 1997 by the WMBA, and is endorsed by the British Bankers Association (BBA).

The Bank of England took on administration of rate in April 2016. Two years later, in April 2018, the rate underwent a number of reforms.[1] In the same year efforts to promote SONIA as the standard Sterling interest rate benchmark for loans, derivatives and bonds were stepped up.[2][3]

Technical details[edit]

Each London business day the SONIA fixing is calculated as the weighted average rate of all unsecured overnight sterling transactions brokered in London by Wholesale Markets Brokers' Association (WMBA) members between 00:00 and 15.15 GMT in a minimum deal size of 25 million GBP with counterparties listed under Section 43 of the UK Financial Services Act 1986.[citation needed]

The rate conventions are: annualised rate, act/365, four decimal places.[citation needed]

In 2018, SONIA (floating rate) bonds accounted for 20.7 per cent share of UK issuance compared to 48.1 per cent share of IBOR (floating rate) bonds.

See also[edit]


  1. ^ a b "SONIA interest rate benchmark".
  2. ^ "Transition to sterling risk-free rates from Libor".
  3. ^ "China discusses ways to stabilize market expectations: central bank". September 3, 2018 – via

External links[edit]