How are BJJ belt promotions decided?

Unlike many martial arts with formal testing and standardized curricula, BJJ promotions are largely at the instructor discretion. This subjective system has advantages and disadvantages. The advantage is that promotions reflect real ability because your instructor watches you roll daily and knows your true skill level. The disadvantage is that criteria vary between instructors. Some emphasize competition results, others value technical knowledge during drilling, and others focus on rolling performance. Common factors include consistent attendance over months or years, demonstrated improvement in technique, ability to effectively roll with people of various sizes and skill levels, understanding of positions and concepts, good attitude and sportsmanship, and contributing positively to the gym community. Stripes on your belt indicate progress within a rank but their meaning varies. Some gyms give four stripes before promoting, others use fewer or none. If you feel you deserve a promotion but have not received one, focus on your training rather than asking for it. Promotions in BJJ are earned, not given.