“Will” after “when” in English

by Jakub Marian

Tip: See my list of the Most Common Mistakes in English. It will teach you how to avoid mis­takes with com­mas, pre­pos­i­tions, ir­reg­u­lar verbs, and much more.

We never use the future tense in time clauses (introduced by phrases like “after”, “as soon as”, “before”, etc.) in English. Should we need to express the idea of something happening, say, after something else in the future, we use the present tense in the time clause and the future tense or a command in the main clause. For example:

correct I will give it to him after he arrives.
wrong I will give it to him after he will arrive.
correct As soon as you get the email, let me know, please.
wrong As soon as you will get the email, let me know, please.

When we use “when” as a conjunction introducing a time clause, the same rule as for other time clauses applies:

correct I’ll call you when I come home.
wrong I’ll call you when I will come home.

In the cases in which “when” doesn’t introduce an adverbial time clause, we do use “will” when expressing the future. Most importantly, we use it when asking questions:

correct When will you know the results?
wrong When do you know the results?

Things get a little complicated when the question is indirect. The “when” part then looks like an adverbial time clause, but it is not. For example, if the original question was, “When will you know the results?”, we can ask:

correct Could you tell me when you will know the results?
see below Could you tell me when you know the results?

The second sentence is grammatical, but it is a different question! In the first case, you ask when (i.e. at what time) the other person will know the results, so the answer would be something like “at 5 o’clock”. In the other case, you ask the person to let you know after they get the results, so they would wait until they get them (e.g. until 5 o’clock) and then tell you, “I just got the results.”

Sometimes, it is harder to see that the structure is that of an indirect question. Consider the following examples:

correct I don’t know when he will come.
see below I don’t know when he comes.

The sentences could be rephrased as:

What I don’t know is: When will he come?
What I don’t know is: At what time does he habitually come?

Both questions are grammatically correct, but only the first one asks about the specific time when “he will come”. The present tense in the other one indicates we ask about what happens habitually (such as every day or every week). The question is in the present because the answer would be in the present too, e.g. “He usually comes at 5 o’clock.”

Finally, “when” can be used to provide further information about a particular point in time. Compare the following two sentences:

I will go jogging tomorrow when there are no cars in the streets.
I will go jogging tomorrow, when there will be no cars in the streets.

They should be understood as follows:

Tomorrow, at a time when there are no cars, I will go jogging.
There will be no cars in the streets tomorrow, which is why I will go jogging.

This article was based on my guide to the most common mistakes in English, which explains many similar topics. Why don’t you check it out?