The Perfect Continuous Tense

The Perfect Continuous Tense (also called the Perfect Progressive) is used to describe actions that are, were, or will be in progress for a period of time up to a certain point. It emphasises both the duration and the continuity of an activity.

General formula:
Subject + (have / has / had / will have) + been + verb‑ing

It has three main forms:

• Present Perfect Continuous – action started in the past and is still continuing now.
  Example: She has been studying for three hours.
• Past Perfect Continuous – action was ongoing up to a specific moment in the past.
  Example: They had been waiting for an hour before the bus arrived.
• Future Perfect Continuous – action will continue until a certain time in the future.
  Example: By next year, I will have been working here for five years.

Common time markers include for, since, all day, by the time, and by + [future time].

In short: Use this tense when you want to highlight how long something has been happening, not just that it happened.