Know what the calendar is doing

The calculation

The converter uses lunar-javascript 1.7.7, with an explicitly documented HKO boundary adjustment for 2057. Inputs are civil dates, not timestamps. Gregorian dates from 1901-01-01 through 2099-12-31 are accepted; a lunar input must convert into that range. Lunar leap months remain separate.

What has been checked

Automated round-trip tests cover all 72,684 Gregorian dates in the supported interval. Separately, 5,982 explicitly labelled dates from 17 Hong Kong Observatory yearly tables are checked in both directions. The sample years are 1901, 1902, 1950, 2000, 2012, 2023–2027, 2030, 2033, 2034, 2057, 2089, 2097, and 2099. This sample is not independent verification of every supported day.

The 2057 boundary

The currently retrieved HKO table puts lunar month 9 of 2057 on September 28; the base library puts it on September 29. NYOO follows the HKO table for this interval: month 8 has 29 days and month 9 has 30. Both directions and the Chinese date labels use the same adjustment. The affected Gregorian interval, September 28–October 27, carries an on-screen note.

Far-future limitations

The HKO warns that new moons and solar terms close to midnight can differ by one calendar day when astronomical estimates change. Its notes identify several future boundaries, including 2057, 2089, and 2097. These dates are a calendar convention based on the current table, not a promise of perfect long-range certainty. Historical calendar practice may also differ from a modern retrospective table.

Zodiac, time zones, and seasons

Zodiac years change at Chinese New Year in this tool. Today is first determined in the selected time zone; that civil date is then converted with the standard Chinese calendar. Solar-term labels follow the library’s standard Chinese-calendar dates, not the exact local instant worldwide. Travel season windows are editorial groupings, not forecasts.

Traditional almanacs

Auspicious and inauspicious activity rules are intentionally disabled. No astronomical source is being used to endorse fortune-telling. Festival labels represent selected traditional observances, not national public-holiday or opening-hour schedules.

Inspectable references

Reference snapshots retrieved 21 September 2026. Test fixtures retain per-year source URLs and SHA-256 hashes. A source refresh must be reviewed, not silently substituted.