A Fed Funds API is a REST endpoint that returns the US federal funds rate as JSON. On Interest Rates API the field is FED_FUNDS (percent, USD). The secured overnight financing rate is SOFR. Call GET /api/v1/latest with a symbols list. Auth is the api_key query parameter.
The official Latest sample is dated 2026-04-20 with FED_FUNDS at 4.33 and SOFR at 4.31 (SOFR’s own observation date in that fixture is 2026-04-19). That is a docs fixture — copy the curl with your key for today’s print. Starter allows 1 symbol per request; the four-symbol JSON below is what Professional and above may request in one call. Docs: interestratesapi.com/docs. Starter is $19/mo (250 requests, 60/min, 90-day max range, 7-day trial).
Request: SOFR on Starter
curl "https://interestratesapi.com/api/v1/latest?symbols=SOFR&api_key=YOUR_KEY" \
-H "Accept: application/json"
Professional and above can pass symbols=FED_FUNDS,SOFR,ECB_MRO,SONIA. Optional category: central_bank, interbank, treasury, reference. Optional base filters by currency and drops everything else — with base=USD, ECB_MRO (EUR) and SONIA (GBP) will not come back.
Response: rates, dates, and currencies
Envelope from the official Latest docs (sample date 2026-04-20 — four symbols, Professional+):
{
"success": true,
"date": "2026-04-20",
"base": "MIXED",
"rates": {
"FED_FUNDS": 4.33,
"SOFR": 4.31,
"ECB_MRO": 2.65,
"SONIA": 4.70
},
"dates": {
"FED_FUNDS": "2026-04-20",
"SOFR": "2026-04-19",
"ECB_MRO": "2026-03-31",
"SONIA": "2026-04-20"
},
"currencies": {
"FED_FUNDS": "USD",
"SOFR": "USD",
"ECB_MRO": "EUR",
"SONIA": "GBP"
}
}
The top-level date is the newest observation in the payload. Use dates.{SYMBOL} per series: SOFR/SONIA are daily; ECB policy rates often land on month-end; FRED’s FED_FUNDS is a monthly average stored on the first of the month. For a daily Fed series use FED_FUNDS_DAILY. Historical docs example: FED_FUNDS = 5.33 on stored date 2025-09-01 when querying 2025-09-15.
MCP for agents
Same key, no second product: point an MCP client at interestratesapi.com/mcp. Each tool call counts as one REST request against the Starter/Professional quota. Use that when an assistant should fetch SOFR instead of you wrapping /api/v1/latest.
Go live with SOFR
1. Register and start the 7-day trial (Starter is $19/mo after).
2. List symbols with GET /api/v1/symbols?category=interbank.
3. Call https://interestratesapi.com/api/v1/latest?symbols=SOFR&api_key=YOUR_KEY
4. Render rates.SOFR and label it with dates.SOFR. Cache to the source cadence (SOFR daily; Fed Funds monthly average).
Support: [email protected].
FAQ: Fed Funds and SOFR API
What is FED_FUNDS vs FED_FUNDS_DAILY?
FED_FUNDS is the monthly average from FRED (stored on the first of the month). FED_FUNDS_DAILY is the daily Fed series. SOFR, SONIA, and €STR are overnight benchmarks in the interbank category.
Can Starter request FED_FUNDS and SOFR together?
No. Starter is 1 symbol per request (2 on /convert). Call twice, or upgrade to Professional ($49/mo, 750 calls).
Is the docs sample today’s SOFR?
No. The Latest sample is dated 2026-04-20 with SOFR 4.31 (observation 2026-04-19). Always hit /api/v1/latest with your key.