Python

import os

import requests

API = "https://api.financecalendarapi.com"
API_KEY = os.environ["FC_API_KEY"]


def get(path: str, **params) -> dict:
    res = requests.get(f"{API}{path}", params=params, headers={"Authorization": f"Bearer {API_KEY}"}, timeout=10)
    if res.status_code != 200:
        problem = res.json()
        raise RuntimeError(f"{problem['code']}: {problem['detail']}")
    return res.json()


# T+2 for a USD trade on the NYSE
print(get("/v1/business-days/add", date="2027-12-23", n=2, calendars="USD,XNYS")["result"])  # 2027-12-28

# Is it a business day in London today?
day = get("/v1/days/today", calendars="XLON", tz="Europe/London")
print(day["is_business_day"])

# Every closure and early close for two calendars in 2027
for cal in get("/v1/holidays", calendars="XNYS,XLON", **{"from": "2027-01-01", "to": "2027-12-31"})["calendars"]:
    for e in cal["entries"]:
        print(cal["id"], e["date"], e["kind"], e["close_time"] or "", e["name"])

For many dates, fetch a calendar’s holidays once and do the arithmetic locally, rather than one request per date: the API counts every request against your plan. pandas users can load format=csv straight into a DataFrame:

import pandas as pd

df = pd.read_csv(f"{API}/v1/holidays?calendars=XNYS&from=2026-01-01&to=2028-12-31&format=csv")