There are literally hundreds of martial arts, and for each the black belt is a standard of excellence. It typically signifies the student is now an instructor and performs at an expert level. Four martial arts stand out for their black belt demands, and Brazilian Jiu Jitsu may be the most demanding. It takes the most amount of time and has the highest level of contact sparring.
Brazilian Jiu Jitsu
Brazilian Jiu Jitsu (BJJ) consists of ground fighting with the goal being to choke, arm-lock or leg-lock an opponent. Progress is based on consistent training time, how well you spar against classmates, and your competition results. The classes can include an hour of contact sparring, which is one reason why it's so tough to earn a black belt in BJJ. A select few of talented instructors have earned it in five years, but it usually takes about 11. A BJJ black belt must be at least 18 years old.
Karate's many divisions have separate black belt requirements. The toughest may be Shodokan Karate, which requires around 75 memorized striking moves. It also calls for four different types of sparring sessions and a kata, a memorized sequence of techniques. One of the harder requirements is to consecutively freestyle spar against two black belts. A student training a couple days a week can get his black belt in three years.
Judo, an Olympic sport as of 2013, involves throwing techniques and a keen awareness of its competition prerequisites. It's high contact and physically demanding, but even that's not enough to get a black belt in judo. You also have to display high moral character and proficiency in all of the lower ranks. You can get one as early as age 14. If you do well at competitions, you can get a black belt in just a couple of years; a non-competitor can do it in six.
Taekwondo originated in Korea and focuses on kicks. The black belt test includes a display of multiple techniques in front of a panel of judges. In addition, you must spar for two minutes, write a three page essay, and break three boards. The flexibility needed for advanced level kicks makes the Taekwondo black belt tough to earn. You also have to put in the time. The International Taekwondo Association requires a minimum of 40 months of training three days every week to be awarded a black belt.