How many hours it will take varies from person to person. Specifically, the following factors affect it. Your ability to learn the language, how you learn it, the tools and training available to you, how different it is from your native language, etc.

It is difficult to say for sure because these factors have a complex impact. However, the following two pieces of information may be helpful.

(1) 900 hours to pass the highest level of the JLPT
The most famous Japanese language test is the JLPT. The administration of the JLPT changed slightly in 2010, but until then, the official website stated that “the time required to pass the highest level is about 900 hours.
The new official website doesn’t have any information about the study time required to pass the exam, but the difficulty level of the highest level is designed to be the same in the old and new administration, so 900 hours is still a good estimate even in the new administration.
*JLPT does not measure writing or speaking ability.

(2) FSI think it takes 2,200 hours to reach native level.
According to the Language Learning Difficulty for English Speakers compiled by the Foreign Service Institute (FSI) of the U.S., Japanese is ranked as the most difficult language for English speakers, along with Arabic, Chinese (Cantonese, Mandarin), and Korean, and requires 2,200 hours to become proficient in daily and professional communication.

In another article, I wrote that it is surprisingly easy to reach the intermediate level, but it still takes time to master.

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