Future time clauses

When you talk about two things in the future, the sentence usually has two parts: a main clause (with will, be going to, an imperative…) and a time clause that starts with when, as soon as, until, before, after… The key rule: the time clause uses a present tense, even though the meaning is future.

The two parts can change places. When the time clause comes first, use a comma; when it comes second, you usually don't need one.

• When I get home, I'll call you.

  time clause first — comma

• I'll call you when I get home.

  time clause second — no comma

💡Many languages use a future form in both parts of the sentence, so learners often say “when I will get home”. In English the future form goes only in the main clause; the part with when / as soon as / until… stays in the present simple: when I get home.

not … until means the action in the main clause will only happen after the other one — not before.

• I won't buy a new phone until this one stops working.

• Don't open the oven until the cake is ready.

After when, after, as soon as, until… you can use the present perfect (have/has + V3) to show that the first action is completely finished before the second one starts. Use the present continuous for something in progress at that time. Just don't use will.

• I'll lend you this book when I've finished it.

  first I finish, then I lend

• When I see Minh, I'll give him your message.

  both happen at about the same time

• You can watch TV after you've done your homework.

• I'll read a book while I'm waiting for you.

  present continuous

With after and as soon as, the present simple and present perfect usually mean the same: after I finish = after I've finished. With when, the two forms can mean different things, as in the examples above.

Both use the present for the future, but the meaning is different: when = you are sure it will happen, it's just a question of time; if = it may or may not happen. See also the lesson “Conditional sentences”.

• I'll call you when I get to the hotel.

  I'm sure I'll get there

• I'll call you if I get lost.

  I may or may not get lost

• When the shop opens, I'll buy some bread.

  it will definitely open

• If the shop is still open, I'll buy some bread.

  I'm not sure it's open

💡To choose between when and if, ask yourself: am I sure it will happen? “I'll let you know when I get the results” (the results will definitely come). “Call me if there's a problem” (there may not be one).

The rule above is only for time clauses. When when starts a question, or a when-clause is the object of a verb (after know, ask, tell me, wonder…) and means “what time”, use will as normal.

• When will you be back?

  a question — will

• I don't know when she'll arrive.

  object of know — will

• Tell me when you arrive.

  time clause — present

• Tell me when you'll arrive.

  asking what time — will

• ✗I'll call you when I will arrive.

  ✓I'll call you when I arrive.

  Use the present in a time clause, not will.

• ✗As soon as she will finish, we'll leave.

  ✓As soon as she finishes, we'll leave.

  After as soon as, use the present simple.

• ✗We won't start until he will come.

  ✓We won't start until he comes.

  After until, use the present simple.

• ✗When he get home, I'll tell him.

  ✓When he gets home, I'll tell him.

  It's still the present simple, so he/she/it needs -s.

• ✗After I'll finish work, I'm going to the gym.

  ✓After I finish work, I'm going to the gym.

  Whatever the main clause is, the after-clause stays present.

• ✗I'll lend you the book when I will have read it.

  ✓I'll lend you the book when I've read it.

  To show “finished”, use the present perfect, not will have.