About SONIA Rates
What is SONIA?
SONIA (Sterling Overnight Index Average) is the effective overnight interest rate paid by banks for unsecured transactions in the British sterling market. It is used as a benchmark rate in sterling markets and is administered by the Bank of England.
How is SONIA Calculated?
SONIA is calculated by the Bank of England through a systematic process that ensures accuracy and reliability:
- Data Collection: The Bank of England gathers data on overnight, unsecured lending transactions from active participants in the Sterling wholesale market.
- Eligibility of Transactions: Only transactions meeting specific thresholds and criteria, including a minimum value, are included in the SONIA calculation.
- Volume-Weighted Mean: SONIA is a volume-weighted mean, meaning larger transactions carry more weight in the final rate.
- Trimmed Mean Method: The Bank of England excludes the top and bottom 25% of transactions to remove the effects of extreme rates.
- Daily Publication: SONIA is published each business day at 9 a.m. (UK time), reflecting activity from the previous business day.
Compounded SONIA Calculation
To calculate the compounded SONIA rate between any two dates, the following formula is used:
Where:
- x = start date of the reference period
- y = end date of the reference period
- d = the number of calendar days in the reference period
The SONIA Compounded Index is calculated as:
Where:
- SONIA Compounded Indexi = The index for date i, calculated and publishing on date i, rounded to eight decimal places (SONIA Compounded Index1 = 100.00000000 published for 23 April 2018)
- SONIA Compounded Indexi-1 = The index for business day i-1, calculated on business day i-1, rounded to 18 decimal places
- SONIAi-1 = The SONIA rate for business day i-1, calculated and publishing on business day i
- ai-1 = The number of calendar days for which SONIAi-1 applies. This is equal to the number of calendar days between business day i-1 and business day i
Our Service
This website provides free access to historical SONIA rate data and includes tools for calculating compound rates. Our goal is to make SONIA rate information easily accessible and usable for financial professionals and researchers.
Note: SONIA RATES is not affiliated with the Bank of England.
API Access
You can access our API directly to calculate SONIA rates in your own applications or Excel spreadsheets.
Holiday Calendars
| Code | Financial Center | Region/Country |
|---|---|---|
| LDN | London | United Kingdom (GB) |
| NYC | New York | United States - New York (US-NY) |
| EUR | Euro Zone | European Central Bank (ECB) |
| AMS | Amsterdam | Netherlands (NL) |
| FRA | Frankfurt | Germany - Hessen (DE-HE) |
| HKG | Hong Kong | Hong Kong (HK) |
| MAD | Madrid | Spain - Madrid (ES-MD) |
| MIL | Milan | Italy - Lombardy (IT-25) |
| PAR | Paris | France (FR) |
| SIN | Singapore | Singapore (SG) |
| SYD | Sydney | Australia - New South Wales (AU-NSW) |
| TOK | Tokyo | Japan (JP) |
| TOR | Toronto | Canada - Ontario (CA-ON) |
| ZUR | Zurich | Switzerland - Zürich (CH-ZH) |
Multiple holiday calendars can be specified using commas (e.g., holidayCalendar=LDN,NYC,EUR). When multiple calendars are specified, a business day must be valid in all specified calendars.
API Endpoint
/api/rate_tableParameters
| Parameter | Description | Format/Options |
|---|---|---|
| startDate | Start date of the calculation period | YYYY-MM-DD |
| endDate | End date of the calculation period | YYYY-MM-DD |
| adjustment | Determines how to handle dates that fall on holidays:
| adjusted |
| dayCountConvention | Day count convention for calculations | ACT/365, ACT/360, 360/360 |
| holidayCalendar | Holiday calendar to use | GB (United Kingdom) |
Example Request
http://soniarates.com/api/rate_table?startDate=2024-09-21&endDate=2024-09-27&adjustment=adjusted&dayCountConvention=ACT/365&holidayCalendar=GB