Will

[Kco13]

On my book is written that we do not use will for things we have already arranged or decided to do like " We are going to the cinema on Saturday" or "I'm not working tomorrow". So why can we say "We will probably go out this evening" or " You can call me this evening. I'll be at home" if both examples are planned ?
Thanks.

[bhaisahab]

On my book is written that we do not use will for things we have already arranged or decided to do like " We are going to the cinema on Saturday" or "I'm not working tomorrow". So why can we say "We will probably go out this evening" or " You can call me this evening. I'll be at home" if both examples are planned ?
Thanks.

There is no fixed rule on that. There is a tendency to use "will" for spur of the moment decisions and "going to" for prearranged activities, but not in all cases.

[Kco13]

So can i also say "You can call me this evening. I'm going to be at home" ?

[bhaisahab]

So can i also say "You can call me this evening. I'm going to be at home" ?

Yes.