United Kingdom Sterling Overnight Average Rate SONIA was at 0.19 percent on Friday January 7. Overnight Interbank Average Rate in the United Kingdom averaged 2.64 percent from 1997 until 2022, reaching an all time high of 8.56 percent in October of 1998 and a record low of 0.04 percent in December of 2020. SONIA (Sterling Overnight Interbank Average Rate) is based on actual transactions and reflects the average of the interest rates that banks pay to borrow sterling overnight from other financial institutions and other institutional investors. Financial businesses and institutions use SONIA in a variety of ways. For example, to calculate the interest paid on swap transactions and sterling floating rate notes . 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. This page includes a chart with historical data for the United Kingdom Overnight Interbank Average Rate.