If you will have vs If you have

Question

If you will have dinner at home, tell me.

or

If you have dinner at home, tell me.

What is the difference between the two sentences? Which one sounds natural?

Answer 1

If you will have dinner at home, tell me.

Here "will" is used with the (slightly archaic) meaning of "wish/intend to", so the sentence is correct, but modern English speakers would generally use "wish/want/intend to" instead, or "would like to".

If you have dinner at home, tell me.

This is a simple sentence that requests you to tell the speaker if you actually have dinner at home, so it is also grammatically correct but conveys a totally different meaning.

Answer 2

I think the second one is correct.

If you have dinner at home, tell.

Although this Source states:

When the situation or action depicted in the if-clause is a result of the main clause, the will-future is used in the if-clause.

He'll pay me $10 if I'll help him do the dishes. (Doing the dishes is the result of paying ten dollars.)

So in any other case, you would not have will/would in an if clause.

In your case, telling him is not the result of having dinner at home, but of planning to have dinner at home.

I hope this explains it correctly.