Symbols / SONIA

SONIA

Sterling Overnight Index Average

Trimmed mean of overnight unsecured sterling transactions. Published daily by Bank of England.

Interbank Active

Country

GBP

Frequency

daily

Update cadence

What is Sterling Overnight Index Average (SONIA)?

Sterling Overnight Index Average is an interbank benchmark rate — the interest rate at which large financial institutions lend to each other on the short-term money market. These rates reflect the cost of liquidity in the banking system and serve as reference rates for a vast range of financial products.

Interbank rates underpin hundreds of trillions of dollars in financial contracts globally — including floating-rate loans, mortgages, interest rate swaps, and structured products. Following the LIBOR transition, overnight rates like SOFR, SONIA, and ESTR have become the new global benchmarks.

Published daily by central banks or banking associations
Calculated from actual overnight transactions
Risk-free rate (RFR) alternative to LIBOR
Used in ISDA derivative contracts

Uses and Related Industries

Primary Industries

Derivatives & Structured Products: Reference rate for interest rate swaps (IRS), forward rate agreements (FRAs), and caps/floors.

Leveraged Finance & CLOs: Floating coupon determination for leveraged loans and collateralized loan obligations.

Securitization: ABS and MBS coupon resets and prepayment model calibration.

Hedge Funds & Prop Trading: OIS discounting, cross-currency basis trading, and LIBOR transition arbitrage.

Corporate Treasury: Short-term borrowing cost benchmarking and cash management strategies.

Specific Applications

LIBOR fallback and IBOR transition replacement rate calculations
OIS discounting for derivatives collateral agreements (CSA)
Floating rate note (FRN) coupon setting and resets
Cross-currency basis swap pricing and hedging
Short-term liquidity management and repo rate benchmarking

API Usage Examples for SONIA

Click each endpoint to see the request URL, parameters, and a sample response.

API Request

https://interestratesapi.com/api/v1/latest?api_key=YOUR_API_KEY&symbols=SONIA

Request Parameters

Parameter	Required	Description
api_key	required	Your API key.
symbols	required	Comma-separated symbol codes. E.g. SONIA

Sample Response

{
    "success": true,
    "date": "2026-05-26",
    "rates": {
        "SONIA": 4.25
    },
    "dates": {
        "SONIA": "2026-05-26"
    }
}

API Request

https://interestratesapi.com/api/v1/historical?api_key=YOUR_API_KEY&symbols=SONIA&date=2026-05-26

Request Parameters

Parameter	Required	Description
api_key	required	Your API key.
symbols	required	Symbol code(s). E.g. SONIA
date	required	Date in YYYY-MM-DD format.

Sample Response

{
    "success": true,
    "historical": true,
    "date": "2026-05-26",
    "rates": {
        "SONIA": 4.25
    }
}

API Request

https://interestratesapi.com/api/v1/timeseries?api_key=YOUR_API_KEY&symbols=SONIA&start_date=2026-05-03&end_date=2026-06-02

Request Parameters

Parameter	Required	Description
api_key	required	Your API key.
symbols	required	Symbol code(s). E.g. SONIA
start_date	required	Start date (YYYY-MM-DD).
end_date	required	End date (YYYY-MM-DD).

Sample Response

{
    "success": true,
    "symbols": [
        "SONIA"
    ],
    "rates": {
        "2026-05-03": {
            "SONIA": 4.25
        },
        "2026-06-02": {
            "SONIA": 4.25
        }
    }
}

API Request

https://interestratesapi.com/api/v1/fluctuation?api_key=YOUR_API_KEY&symbols=SONIA&start_date=2026-05-03&end_date=2026-06-02

Request Parameters

Parameter	Required	Description
api_key	required	Your API key.
symbols	required	Symbol code(s). E.g. SONIA
start_date	required	Start date (YYYY-MM-DD).
end_date	required	End date (YYYY-MM-DD).

Sample Response

{
    "success": true,
    "fluctuation": {
        "SONIA": {
            "start_rate": 4.25,
            "end_rate": 4.37,
            "change": 0.12,
            "change_pct": 2.8235
        }
    }
}

API Request

https://interestratesapi.com/api/v1/ohlc?api_key=YOUR_API_KEY&symbols=SONIA&start=2026-05-03&end=2026-06-02&period=monthly

Request Parameters

Parameter	Required	Description
api_key	required	Your API key.
symbols	required	Symbol code. E.g. SONIA
start	required	Start date (YYYY-MM-DD).
end	optional	End date (YYYY-MM-DD). Defaults to today.
period	optional	Grouping: monthly (default), weekly, quarterly.

Sample Response

{
    "success": true,
    "symbol": "SONIA",
    "period": "monthly",
    "ohlc": [
        {
            "period": "2026-05",
            "open": 4.25,
            "high": 4.5,
            "low": 4.15,
            "close": 4.37,
            "data_points": 21
        }
    ]
}

API Request

https://interestratesapi.com/api/v1/convert?api_key=YOUR_API_KEY&from=SONIA&to=FED_FUNDS&amount=1

Request Parameters

Parameter	Required	Description
api_key	required	Your API key.
from	required	Source symbol. E.g. SONIA
to	required	Target symbol. E.g. FED_FUNDS
amount	required	Amount to convert.
term_months	optional	Term in months for interest calculation (default 12).

Sample Response

{
    "success": true,
    "from": "SONIA",
    "to": "FED_FUNDS",
    "amount": 1,
    "result": 0.981524
}

Replace YOUR_API_KEY with your key Get a free API key →

Factors Influencing SONIA

Market Factors

Short-term liquidity demand and supply in the banking system
Bank credit risk and perceived counterparty default probability
Central bank reserve requirements and corridor system
Repo market activity and secured lending rates

Technical Factors

Spread over central bank policy rate (LIBOR-OIS spread)
Excess reserves held at the central bank
Dealer balance sheet capacity at quarter/year-end
Options market volatility and hedging flows

External Factors

Regulatory changes (Basel III/IV liquidity coverage ratio)
Central bank open market operations and asset purchases
Systemic stress events and flight-to-quality flows
IBOR transition and LIBOR cessation timeline

Other rates from GB

BOE_BANK_RATE

Bank of England Official Bank Rate

Other Interbank rates

SOFR

Secured Overnight Financing Rate

TIBOR_3M

TIBOR 3 Month

BBSW_3M

BBSW 3 Month

CORRA_3M

Canadian 3-Month Interbank Rate

KORIBOR_3M

KORIBOR 3 Month

JIBAR_3M

JIBAR 3 Month

Symbol Details

Symbol: SONIA
Category: Interbank
Country: GB
Currency: GBP
Provider: fred
Frequency: daily
Series ID: IUDSOIA
Unit: percent

Access SONIA via REST API

Get live and historical Sterling Overnight Index Average data in JSON format. One API, 50+ countries, normalized.

Get Free API Key View API Docs

GET /api/latest?symbols=SONIA

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