What is the udaya tithi?

The tithi current at local sunrise. The civil calendar names each day after it, which is why a day can be labelled with one tithi while most of its hours belong to the next.

What is a karma-kala?

The part of the day in which a festival's rite is performed, such as sunrise, midday, the afternoon, the evening after sunset or midnight. A festival is kept on the day its tithi covers that window.

Which festivals follow which window?

Examples: Laxmi Puja follows pradosha (evening), Bhai Tika and Vijaya Dashami follow aparahna (afternoon), Krishna Janmashtami and Maha Shivaratri follow nishita (midnight), and many vratas and Ghatasthapana follow the sunrise tithi.

What happens when the tithi covers the window on both days, or on neither?

Each festival's rule names a tie-break: purva, the earlier day, or para, the later day. The rationale shown on festival pages states which tie-break was used.

Why do official notices sometimes differ from computed dates?

Authorities such as the Nepal Panchanga Nirnayak Samiti weigh classical texts and local custom. When a recorded notice differs from the engine, this site shows the official date and keeps the computed date beside it.

How a festival date is decided: the sunrise tithi versus the ritual window