Nager.Date has earned its reputation in the .NET community as a reliable, free public holiday API. With over 1,300 GitHub stars, 90 contributors, and MIT licensing, it's a well-maintained open source project that handles European holidays exceptionally well.

But if you're building applications that serve users outside Europe — particularly in the Middle East, North Africa, or Southeast Asia — you'll run into gaps. This comparison helps you understand when Nager.Date is the right choice and when World Data API makes more sense.

Nager.Date covers 119 countries with a strong focus on Europe, North America, and parts of Asia-Pacific. If your application serves users primarily in these regions, you're well covered.

World Data API covers 230+ countries, filling in gaps across Africa, the Middle East, Central Asia, and smaller island nations. The difference matters when you're building for a global user base or operating in emerging markets.

This is where the two APIs diverge significantly.

Nager.Date explicitly excludes all Islamic lunar calendar holidays — Eid al-Fitr, Eid al-Adha, and related observances. Their documentation explains why: these holidays depend on local moon sightings and can vary by location and religious authority.

This is a reasonable technical decision for an open source project. Lunar calendar holidays are genuinely difficult to handle with precision.

World Data API takes a different approach: it includes Islamic holidays using astronomical calculations. These calculated dates may differ from actual observed dates by 1-2 days in some locations, since local religious authorities sometimes make last-minute adjustments based on moon sightings.

For many applications, calculated dates are sufficient. You can display them with appropriate caveats or use them for planning purposes. But if your application requires exact observance dates for a specific religious community, you may still need to verify against local announcements.

Why this matters: Islamic holidays are public holidays in 50+ countries. If you're building a scheduling app, HR system, or logistics platform that serves users in Indonesia, Malaysia, UAE, Saudi Arabia, Egypt, Turkey, Pakistan, Bangladesh, or Nigeria — Nager.Date won't give you the data you need.

Both APIs support regional holidays, but with different scope.

Nager.Date provides subdivision data for 13 countries: Australia, Austria, Brazil, Canada, Germany, Italy, Liechtenstein, Netherlands, New Zealand, Spain, Switzerland, UK, and USA.

World Data API offers broader subdivision coverage, which becomes relevant when you need state-level or province-level holiday data for countries outside this list.

Nager.Date categorizes holidays into six types: Public, Bank, School, Authorities, Optional, and Observance. This granularity is useful when you need to distinguish between days when banks close versus days when schools close.

World Data API provides similar categorization with its own taxonomy.

If you need to calculate "the next business day" or "10 business days from now," World Data API includes this functionality. Nager.Date focuses on holiday data — you'll need to build business day logic yourself.

World Data API bundles holiday data with related datasets: regions, cities, timezones, astronomy data, and travel reference data (power plugs, emergency numbers, climate averages). If you're already using World Data API for other purposes, adding holiday data requires no additional integration.

Nager.Date is purpose-built for holidays. If that's all you need, its focused approach keeps things simple.

The REST API is completely free with no rate limits, no API key required, and CORS enabled. For hobby projects and low-stakes applications, this is hard to beat.

For offline use via NuGet packages or Docker containers, you'll need a license key obtained through GitHub sponsorship. This supports the project's ongoing development.

All paid tiers have a 1,000 requests/hour rate limit.

Nager.Date is the better choice when:

• Your users are primarily in Europe, North America, or Australia

• You're building a hobby project or internal tool

• You want zero cost and no API key management

• You prefer open source with the option to self-host

• You don't need Islamic holiday data

• You're already in the .NET ecosystem and want NuGet integration

World Data API makes more sense when:

• You're serving users in Muslim-majority countries

• You need holiday data for 119+ countries

• Business day calculations are a core requirement

• You're already using World Data API for other data (timezones, regions, etc.)

• You need a single API for multiple data types

• You're building a production application with global reach

If you're currently using Nager.Date and considering a switch, the migration is straightforward. Both APIs return similar data structures — country codes, holiday dates, names, and types. The main work is updating your API calls and handling authentication.

You might also consider using both: Nager.Date for European holidays (where it excels) and World Data API for regions it doesn't cover. This hybrid approach adds complexity but minimizes costs.

Nager.Date is a quality open source project that does exactly what it promises. For European-focused applications and projects where cost is the primary concern, it's an excellent choice.

World Data API is the step up when you need global coverage, Islamic holidays, or business day calculations. The 230+ country coverage and calculated lunar calendar support make it suitable for production applications serving diverse, international user bases.

The decision often comes down to geography: if your users are in the 119 countries Nager.Date covers and don't observe Islamic holidays, stick with the free option. If you're building for a global audience, World Data API fills the gaps.