までにBy ~, By the time that ~, Before ~

までに is a combination of two different types of particles. The adverbial particle まで, and the case marking particle に. までに is very similar to まで when it means 'until'. However, there is one very important distinction. This distinction is that までに means 'by', not 'until'.

To use までに, we will need to attach it to the end of a noun, or verb in the non-past form.

To understand the difference between まで, and までに, we need to remember that に usually marks a 'target', or a 'destination' for where something will happen. In this case, まで is the 'target' that に is marking. This is due to the fact that まで means 'as far as' (まで is sometimes written using kanji 迄(まで), especially in older/formal texts, and newspapers).

In this way, までに more literally means '(A) as far as (に marks the target), (B).

Fun Fact

Originally, まで meant 'as far as' in regard to the passing of a particular event. However, in modern Japanese, most people will assume that the speaker means 'by the beginning of (A)'. Due to this, sentences that have a very broad event, such as 夏(なつ)までに could actually be interpreted as 'by the start of summer', or 'before the end of summer', depending on who you are talking to. In these cases, it would be better to add a more specific time frame.