Many language learners wonder how many months or years it will take to become fluent in their target language, but the length of time is best measured in hours. Two people can both study a language for six months, but if one of them studies for two hours a day, that person will learn more if the other one is only studying for half an hour a day. The language you’re studying also has an effect on how long it will take. A language which is closely related to English, like Swedish, will take fewer hours than one which is very different, like Mandarin.
So how many hours does it take? According to ACTFL, it takes 720 hours to reach an advanced level of a closely related language, 1320 hours to reach the same level of a somewhat more distant language like Finnish or Russian, and at least 2400 hours to reach the same level of a very distant language like Chinese or Japanese. They also estimate that if you were studying these languages full-time, you could learn a foreign language to an advanced level anywhere between six months to two years, depending on the language.
However, as few people are able to take enough time to study a language full-time, the number of hours is a much better measure. If you took an hour a day, every day, to study French, you could reach an advanced level in two years. But it would take about seven years to reach the same level in Chinese or Japanese if you only studied for an hour a day. No matter how long it takes in the end, every bit of time spent studying is working towards fluency.