Meaning of “be about to do something”

Form:
be about + infinitive

The infinitive = “to” + the base form of a verb.

Meaning:
To describe something that we expect to happen very soon.
It refers to the immediate future.

Examples:

The bus is about to leave.
(The bus is going to leave very soon.)

Manager: The meeting is about to start. Where is everyone?

Jane: Could you help me with the sales report?
Sarah: I’m about to leave. Can we do this tomorrow?

Customer: What is the price of the laser printer?
Supplier: I am about to send you an email with all of our prices.

be just about

Form:
be just about + infinitive

Meaning:
The word “just” emphasises that the future action is very very soon. Probably in the next few seconds.

Example:

Jane: Let’s watch this TV show.
Mark: No sorry, I’m just about to go to bed.

Form:
past form of be + about + infinitive

Meaning:
Something that was going to happen but did not happen.

Examples:

Clare: I was about to eat when you invited me for a drink.

Jane: Hi Sarah!
Sarah: Hi Jane! I was just about to call you.