The Vietnamese lunar calendar for the whole family

In Vietnamese families, the dates that matter most move every year. A grandparent’s death anniversary, Tết, the full moon offering: they all follow the lunar calendar, so they land on a different day of the solar calendar each year. Someone in the family has to remember, and tell everyone else. For families living abroad it is even harder.

Nhật Nguyệt is the app we built for that.

What it does

• Lunar reminders that repeat correctly. Set a death anniversary once, and it lands on the right solar date every year, including leap months.

• Family groups. Shared reminders, a plan for each occasion, comments and a photo album per event.

• Everywhere you look. Home-screen widgets on Android and iOS, Wear OS and Apple Watch, Google Calendar sync, and a web version.

• Living abroad? Choose whether the calendar follows Vietnam time or your local time.

• Three languages: Vietnamese, English and Chinese.

What makes it different

• The lunar calculations are cross-checked against NASA new moon data and IMCCE solar term data. The results are published as open datasets on Hugging Face and GitHub, with a DOI on Zenodo.

• Over 1,500 articles on Vietnamese customs and traditional knowledge, each with references. We label what is calendar fact, what is folk belief, and where different schools disagree.

• The AI assistant answers from our published articles and cites them, instead of making things up.

The app is free to use. An optional plan adds larger groups and more features.

We would love your feedback, especially from anyone who keeps track of lunar dates for their family. What would you want a calendar like this to do?