Mi pasaporte está a punto de caducar, así que debo renovarlo.

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Breakdown of Mi pasaporte está a punto de caducar, así que debo renovarlo.

• mi: my
• estar: to be
• deber: must

Questions & Answers about Mi pasaporte está a punto de caducar, así que debo renovarlo.

Why does the sentence use está (from estar) and not es (from ser)?

Because estar is used for states/conditions that are seen as temporary or changeable. Being a punto de (about to) something is a temporary situation, so Spanish naturally uses estar: está a punto de caducar. Using ser here would sound wrong.

How does estar a punto de + infinitive work, and what exactly does it mean?

Estar a punto de + infinitive means to be about to + verb (something is imminent).
Structure:

• estar (conjugated) + a punto de
  • infinitive
    Example from the sentence: está a punto de caducar = is about to expire.

Why is there a de after a punto?

It’s fixed idiomatic grammar: a punto de + infinitive. You don’t drop the de.
So you say a punto de caducar, a punto de salir, a punto de llover, etc.

What does caducar mean here, and is it the same as expirar?