“Posh Dasam” in this Jain (Vikram Samvat / Gujarati) year falls on:

Posh Dasham (Magshar Vad 9) ➡️ Saturday, 13 December 2025 (Gregorian date)

So for the English year 2026 there is no separate Posh Dasam; it comes just before, on 13‑12‑2025, and is especially observed for Shri Parshvanath Bhagwan Janma & Diksha Kalyanak in many Jain sanghs.