Identify the exact date and time of death
Determine the lunar day at the place and time of death using a Panchang or Hindu calendar
Note the tithi active at the moment of death
If the death occurred near a tithi change, verify the exact transition time
Use the tithi name and number from the lunar calendar for that date and time
For annual remembrance, observe the same tithi in the same lunar month each year
If the exact tithi is unclear, consult a qualified priest or astrologer with the death time and location