There are hundreds of useful phrases that can help English learners show relationships between the past and present, but we often only recognize them when students stumble. Until now is one of these. Without this useful adverbial phrase, it is difficult to articulate something that was true for a period up to the present point but that has changed at the time of speaking or writing.
To incorporate until now into their repertoire, learners should know that the adverbial phrase is not used with simple present, present progressive, or any type of future verb. Also, although it routinely appears with a positive verb (Until now, the washing machine was working fine.), it is often associated with negative verbs (I didn’t know until now that you were feeling sick.). To help students understand these parameters of use, try a consciousness-raising activity to help them notice the pattern. This can be followed by a scaffolded activity that encourages feedback on their understanding, and then a more open-ended practice.
Once students have a sense of when and how to use until now, it can be contrasted with other similar forms such as so far. However, in my experience, it’s dangerous to contrast the two in the initial presentation because A) learning two similar phrases at the same time can cause learners to confuse them, and B) the two phrases are not synonymous in terms of function and would likely be found in different conversations.
For now practice with Until now, check out the downloadable activity.