caldays
Open data

caldays open datasets — free, citable, well-sourced.

Eight open datasets covering 206 countries — public holidays, long weekends, time zones, solar/lunar astronomy, and prayer times. All released under Creative Commons Attribution 4.0. Free for commercial and academic use.

Headline

At a glance

Datasets
8
Free + open
Countries covered
206
Public holidays
License
CC BY 4.0
Commercial use OK
API requests
10k/day
Per-IP fair use, no key
The datasets

8 open datasets

Public holidays (per country, per year)
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National public holidays for 206 countries, 1900–2049. Each entry includes date, name, type (national / joint / regional).

GET /v1/{cc}/holidays/{year}

Sources: Government gazettes, central-bank holiday calendars, official tourism boards

Long-weekend index
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Computed long-weekend opportunities per country per year. Includes start/end, total days, bridge-day flag.

GET /v1/{cc}/long-weekends/{year}

Sources: Derived from public holidays + weekend definitions

World clock & time zones
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Current local time, UTC offset, DST transitions, and time-zone metadata for 800+ cities.

GET /v1/clock?cities=jkt,sgp,tyo,lon

Sources: IANA tz database (tzdb), city geo lookups

Sunrise, sunset & twilight
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Precise sunrise, sunset, and civil/nautical/astronomical twilight times for any city. NOAA solar position algorithm.

GET /v1/sun/{city}/{date}

Sources: NOAA Solar Position (Reda & Andreas 2003)

Moon phases & illumination
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Full-moon, new-moon, first/last-quarter dates with arcminute-precision illumination percentage. Jean Meeus algorithm.

GET /v1/moon/{year}

Sources: Jean Meeus, Astronomical Algorithms 2nd ed.

Eclipses (solar & lunar)
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50+ eclipses, 2020–2030. Type, magnitude, peak time, visibility region.

GET /v1/eclipses/{year}

Sources: NASA Eclipse Bulletin (Espenak)

Mercury retrograde
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Mercury retrograde periods with start/end dates. Keplerian elements + light-time correction.

GET /v1/mercury-retrograde/{year}

Sources: JPL/Standish Keplerian elements

Prayer times (Islamic)
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Five daily prayer times for any city. Multiple calculation methods (MWL, ISNA, Egypt, Karachi, Umm al-Qura).

GET /v1/prayer-times/{city}/{date}

Sources: Computed via standard angles; user-selectable method

License

Free to use, with attribution

All caldays open datasets are released under Creative Commons Attribution 4.0 (CC BY 4.0).

You may copy, redistribute, transform, and build upon the data for any purpose, including commercial — provided you credit caldays with a visible link.

Suggested credit: Holiday & calendar data: caldays.com (CC BY 4.0)

For researchers

How to cite caldays in academic work

APA: caldays. (2026). caldays open holiday and calendar datasets. https://caldays.com/open-data
BibTeX:
@misc{caldays2026,
  title  = {caldays open holiday and calendar datasets},
  year   = {2026},
  url    = {https://caldays.com/open-data},
  note   = {CC BY 4.0}
}

Frequently asked questions

Is the data really free for commercial use?
Yes. CC BY 4.0 explicitly permits commercial use. You can build a paid product on top of caldays datasets without paying us — we only ask for visible attribution with a link.
How accurate is the holiday data?
caldays cross-references at least two primary sources per country (government gazette + tourism board or central bank). When sources disagree, we side with the official gazette and note ambiguity in our changelog.
Do you provide historical data?
Public holidays: yes, 1900–2049 (algorithmic for movable feasts where deterministic; otherwise clamped to verified windows). Astronomy: yes, full Meeus / NOAA range. Time-zone history: via IANA tzdb.
Is there a paid tier?
The data is free under CC BY 4.0. We offer paid API tiers ($29/mo for 100k req/day, $199/mo for 10M req/day, attribution waiver included) for high-volume commercial use — but you do not need a paid plan to use the data.
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Open data
8 datasets · 206 countries · CC BY 4.0