For more information, and any errata, see the site http://www.calendarists.com.

WARNINGS

1. We have been careful to insure that our conversion functions work for at least 10,000 years before/after the present, but the Chinese code, for example, will not work for the 200th century.
2. The astronomical code we use is not the best available. Hence, positions and times of astronomical evenets are only approximate. More precise code would be more time-consuming and complex and would not necessarily yield in more accurate results for those calendars that depended on observations, tables, or less accurate calculations. Thus, the correctness of a date on any of the astronomical calendars is contingent on the historical accuracy of the astronomical code used in its calculation. In particular, the Observational Islamic code (based on visibility from Cairo) can only approximate actual practice.
3. The modern Hindu calendars are subject to many regional differences.  Our code follows one variant.
4. All of our functions give "correct" (mathematically sensible) results for negative years and for dates prior to the epoch of a calendar. However, these results may be culturally wrong. In particular, year 0 is assumed to exist for all calendars except the Julian and the Persian.
5. We have chosen not to optimize the algorithms at the expense of clarity; consequently, considerable improvements in economy are possible.
6. Checking the results of conversions against the historical record is sometimes misleading because the different calendars begin their days at different times. All of our conversions are as of noon.