grammaticality - Is it correct to say "we start tomorrow"?

Here's an example of a short conversation between me and a native speaker via text messages:

A: I'm so exited for this app
B: Yeah, me too
A: We start tomorrow
B: OK

Shouldn't it be "We are starting tomorrow"?!

Answer

No, it doesn't need to be we are starting tomorrow

In a very brief and general way, there are four ways to talk about the future in English:

• 
  

  Using will as in I will answer the door. This is usually used for instantaneous decisions.

  
  


• 
  

  Using going to as in I am going to buy a new car. This is usually used for plans.

  
  


• 
  

  Using present continuous as in I am buying a new car. This is usually used for arrangements.

  
  


• 
  

  Using present simple, as in I get my new car this afternoon! This is usually used for things that are scheduled or on a timetable.

  
  

As a sequence, you decide you need a new car - I'll buy a car; then you tell everybody about your plan - I'm going to buy a car; then you go to the showroom, pick one out, and arrange to pay for it - I am buying a new car; then everything is finalised and they tell you the date and time when you can go to collect it - I get my new car next week.

This is not a random thing. It does make sense. Will because it is your will that you should have a car. Think of writing a will before you die. Going to because you have a target - a new car - that you are moving towards. Present continuous because you have begun the process of obtaining a new car. Present simple when it has become as good as a fact.