One of the most common questions when first starting to learn Japanese is “How Long does it take to learn Japanese?”  But the the question is so non-specific as to make any answer meaningless.  For example, usually the answer is given in years with no regard to the actual amount of studying – Clearly it will take more years of study 1 hour per day than it will take someone studying full time.  I find it much more useful putting the answer in terms of hours of study and then we can get a more consistent and useful answer.

Another reason you will get varying answers to “How long does it take to learn Japanese?” is how do you know when you’ve learned Japanese?  Is it when you can order from a Japanese dinner menu in broken Japanese, or is it when you feel comfortable having a job interview completely in Japanese?  Clearly different amounts of study are required.

Accumulating the significant amount of vocabulary required to understand Japanese is the primary task when learning Japanese.  Typical learners can memorize and review roughly 5-10 words(kanji included) per hour of actual study.  So we can (very roughly) calculate the amount of hours it would take to achieve various levels of proficiency:

~1k words (100 – 200 hours of study)
can recognize familiar words on TV
however no real understanding of what’s going on in even the most basic Japanese conversation.

2k words  (200 – 400 hours of study)
~ 80% coverage
can follow along(with extreme difficulty)  simple Japanese media (NHK Easy news, Simple Anime)

3k words   (300 – 600 hours of study)
~ 85% coverage
Getting Easier to consume beginning Japanese media (sukinayo..)

4k words  (400 – 800 hours of study)
Moderate difficulty following regular Japanese(nhk, psycho pass..)
Can follow along with basic anime (Shirokuma cafe, pokemon)
Can understand about 80-90% of a regular NHK news article and 90-95% of an NHK easy article.
can read young adult graphic novel (Kino no Tabi) about 90%

6k words (600 – 1,200 hours of study)
~ 90% coverage
Can read 80-90% of words in a Japanese magazine or newspaper depending on how technical
Difficulty producing even known words in conversation.

7k words (700 – 1,400 hours of study)
Can read Japanese novel with minimal look-ups

10k words (1,000 – 2,000 hours of study)
~ 95% coverage
Can read interesting articles and have meaningful conversations.

20k words (2,000 – 4,000 hours of study)
~99% coverage

US Department of State Estimate:

The Foreign Service Institute (FSI) of the US Department of State has compiled approximate learning expectations for a number of languages based on the length of time it takes to achieve General Professional Proficiency in Speaking and Reading.  According to the FSI, Japanese is a category III language, meaning that it is among the most difficult for an English speaker to learn.  Category III languages require twice as much time as category II and four times as much study time as category I languages. They estimate that it would take 2500 hours of study to achieve General Professional Proficiency with half of the time spent inside Japan.

JLPT Estimate:

If you have a specific JLPT level in mind, here are some estimates for time involved in studying for various levels:

New test content summary
Numbers estimated from released JEES documentation.

Level	Kanji	Vocabulary	Ability	Incremental Hours of Study
N5	~100	~800	Can understand classroom phrases with hiragana and very simple kanji. Can understand patterned phrases and glean needed information.	150 (estimated)
N4	~300	~1,500	Can understand daily-life conversations, if spoken slowly. Can read simple materials aimed at non-native speakers.	300 (estimated)
N3	~650	~3,750	Can understand native materials if rewritten with simplified vocabulary and kanji. Can follow everyday conversations at natural speed.	450 (estimated)
N2	~1000	~6,000	Can read written materials on general topics and understand conversations and news at natural speed.	600 (estimated)
N1	~2000	~10,000	Can understand speech in a variety of challenging situations. Can grasp nuance and progression of ideas in abstract and complex materials.	900 (estimated)