What is a leap month?
An extra month is not the same thing as February 29.
Source-linked guide · Updated 28 September 2026The Chinese calendar combines lunar months with the solar year. Some lunar years include an additional, intercalary month. In this tool it is labelled “Leap month” and is listed separately from the ordinary month with the same number.
A concrete example is 2025: ordinary month 6 begins on June 25, while leap month 6 begins on July 25. They are different dates, even though both use the number six. Selecting the wrong one changes the result by roughly a month.
Choose the year before choosing a lunar month. NYOO lists only the months that exist in that year and rejects days beyond the selected month’s length. A leap Gregorian day and a leap lunar month solve different calendar problems; neither can stand in for the other.
Sources & further reading
Sources checked 21 September 2026. Written with AI assistance, reviewed by the owner, and checked against the linked material.