A SONIA vs SOFR rate API returns the two overnight benchmarks side by side: Sterling SONIA and USD SOFR. On Interest Rates API those symbols are SONIA and SOFR on GET /api/v1/latest with query api_key.
Starter is $19/mo (1 symbol per latest request, 250 calls) with a 7-day trial. Professional ($49) can pass both in one call. Do not send base=USD if you need SONIA (GBP). MCP: interestratesapi.com/mcp.
Request: Starter (one symbol each)
curl "https://interestratesapi.com/api/v1/latest?api_key=YOUR_API_KEY&symbols=SONIA"
curl "https://interestratesapi.com/api/v1/latest?api_key=YOUR_API_KEY&symbols=SOFR"Response: official Latest mix (2026-04-20)
{
"rates": {
"SOFR": 4.31,
"SONIA": 4.70
},
"dates": {
"SOFR": "2026-04-19",
"SONIA": "2026-04-20"
},
"currencies": {
"SOFR": "USD",
"SONIA": "GBP"
}
}Starter returns one symbol per body. Dates can differ per series. Convert (from=SOFR&to=EURIBOR_3M) is a different path if you need a loan spread.
Go live
1. Register — 7-day trial.
2. Copy api_key.
3. GET latest twice on Starter, or both symbols on Pro.
4. Label dates.SONIA / dates.SOFR. No base=USD.
