People often use expressions like "in 2 weeks" approximately. So it can be hard to know if someone means exactly 2 weeks or about 2 weeks. When you want to specify an exact day, use phrases like "a week from tomorrow" or "two months from today":

The school dance is only a week from tomorrow. Do you have anyone to go with?

This works for talking about the future. Talking about the past uses a different phrase:

We first met four years ago today.