The card will be sent to you at a future date.

This policy will affect the future course of action.

We do it for future generations!

Of course, the logic stays the same even after the preposition “in”, which is probably the most confusing case for non-native speakers:

When “future” is used as a noun, the situation gets a little more complicated. When “future” means “the time or the events that will come after the present”, it is always used with the definite article:

The phrase “in the future” in AmE and BrE

The phrase “in (the) future” has two meanings. When it means “at a future point in time”, it is used with the definite article:

However, when it means “from now on”, there is a divide between American English and British English. An American would still say “in the future”, as in the previous case, whereas a Brit would likely say “in future” (with no article). Thus, “from now on, please, be more careful” could be rephrased as

If you speak American English, you don’t have to care about the distinction. However, if you speak British English, using “in future” instead of “in the future” can completely change the meaning of a sentence. Compare

and

The latter statement is definitely false, while the former one is probably true.