Do not watch every episode blindly. If you want the core story (Canon), watch roughly 303 episodes . If you want the full experience including the canon filler, prepare for a long haul through 500 episodes across 21 seasons .
Unlike modern anime that release in 12 or 24-episode blocks, Naruto Shippuden aired continuously for years. The "21 Seasons" categorization is the most common on platforms like IMDb and international TV guides. naruto shippuden how many seasons