Tithi anniversary calculator
A yearly observance follows the tithi — the lunar day — not the Gregorian date. Give the original date and we work out which tithi it was, then the civil day that tithi returns on for New Delhi.
What this is for
Shraddha and tithi-anniversary observances recur on the lunar day, so the Gregorian date is different every year. This finds it. It is a calendar calculation: no chart is cast and nothing is predicted.