To add to what others have said, there really are too many factors that can work together to allow one to figure out the definition of a word, many of which are not directly related to proficiency.
It can depend on how many of the others words you know. If you read a sentence where a single word is unknown, you obviously have an advantage to if you only know half of the words. For example, in English, if I give you the sentence: "the small ___ barked at the cat", then it is reasonable to guess that the blank should be "dog", because the verb "bark" is only commonly used with dogs.
It can also depend on how much you already know about a given topic. If you have extensive knowledge about cooking, and are watching a cooking show in a foreign language, you will have an advantage to someone who knows little about cooking. In topics with highly specialized terms, like science or mathematics, having previous knowledge may be essential to determining the meaning. For example, even a native speaker of English will likely not be able to determine the meaning of the sentence "lung adenocarcinoma distally rewires hepatic circadian homeostasis" without an already existing knowledge of common biological and medical terms.
It can depend on how similar a foreign language is to a native language. For example, if one's native language is from the Germanic family, then the word "wasser" (water) in German is likely easier to understand than the word "mizu" in Japanese.
Lastly, it can depend on the specific language you are learning. If the unknown word is derived from other words you already know, then it will obviously be easier to determine its meaning. The more a language does this, the easier it will be to learn new words without looking them up. In Esperanto, if you know the word "bona" (good) and some basic grammar, then the meaning of the verb "plibonigi" (to improve) will be obvious, even if you never heard the word before. Sometimes, the way a language is written can help also. In Japanese, if you know that the character 神 (kami) means "god" or "divine" and the character 学 (gaku) means "learning" or "study", then it may be easy to determine when reading that 神学 (shingaku) means "theology", or "the study of god", even if you never seen that word before.
All of this can also be further complicated by the use of idioms. For example, it is likely impossible to determine the meaning of the English phrase "kick the bucket" (to die) without looking it up or being exposed to it a number of times.
The best way to be certain you are properly understanding a language is to learn as much as you can. The more you know, the more will become clear. However, it is impossible to say how much you will need to know. It could take 1 month or several years before you are confortable, depending on the language and on your previous knowledge.