How do I get the calendar-year returns of a fund by ISIN?

Where it is in the response

Sample for iShares Core MSCI World UCITS ETF (IE00B4L5Y983):

json
"calendarReturns": {
  "years": ["2020", "2021", "2022", "2023", "2024", "2025"],
  "fund": [15.9, 21.9, -18.0, 23.9, 18.7, 21.2],
  "benchmark": [15.9, 21.8, -18.1, 23.8, 18.7, 21.1]
}

Where the figure comes from

The three arrays mirror the discrete-performance table that KIDs and factsheets must print, in the same order. Where the fund house also publishes the NAV history, the years are checked against it. The ongoing year is not included until it closes.

The request

bash
curl -s --max-time 300 https://fundfactsapi.com/api/v1/funds/IE00B4L5Y983 \
  -H "Authorization: Bearer $FUNDFACTS_API_KEY" | jq '.data.calendarReturns'

python
import os, requests
r = requests.get("https://fundfactsapi.com/api/v1/funds/IE00B4L5Y983",
                 headers={"Authorization": f"Bearer {os.environ['FUNDFACTS_API_KEY']}"}, timeout=300)
fund = r.json()
print(fund["name"], fund['data']['calendarReturns']['years'])

javascript
const res = await fetch("https://fundfactsapi.com/api/v1/funds/IE00B4L5Y983", {
  headers: { Authorization: `Bearer ${process.env.FUNDFACTS_API_KEY}` },
  signal: AbortSignal.timeout(300_000),
});
const fund = await res.json();
console.log(fund.name, fund.data.calendarReturns.years);

Sign up at fundfactsapi.com/signup for a key; the Free plan is 15 lookups a month with no card. Without a key, GET https://fundfactsapi.com/api/v1/demo/funds/IE00B4L5Y983 returns the same payload for funds already in the store (30 calls a minute per IP; it never loads a new fund).

Caveats

• Returns are in the share-class currency, as the document states them.
• A young fund has fewer years; a fund launched mid-year has no partial first year unless the document prints one.

Several funds at once

POST /funds with { "isins": ["…", "…"], "wait": true } returns the same payload for up to 10 ISINs per call on Starter, 50 on Pro and 200 on Scale. One request is counted per ISIN answered. X-RateLimit-Remaining on every response tells you how many are left this month; a 429 rate_limited response carries Retry-After. Search and /me are free.

A fund nobody has requested in the last 24 hours is loaded on demand from the documents the fund house publishes. That first call takes 15 seconds to about 3 minutes; set your client timeout to 300 seconds and do not fire a second request for the same ISIN while the first is running. Every later call within 24 hours returns from the store in well under a second with cached: true.

Everything else in the payload is listed in the field reference.