On which day of Pitrupaksha 2026 should I perform Shraddha for my father?

Perform Shraddha for your father on the lunar tithi that corresponds to the tithi on which he passed away. For example, if your father died on a Panchami tithi, perform his Shraddha on the Panchami day of Pitrupaksha. If you do not know the exact tithi, or if you want to be comprehensive, perform rites on Sarva Pitru Amavasya (October 10) — this day covers all ancestors regardless of their death tithi.