FUTURE PERFECT CONTINUOUS

Future Perfect Continuous has two different forms: "will have been…" and "be going to have been…" Unlike Simple Future forms, Future Perfect Continuous forms are usually interchangeable.

FORM Future Perfect Continuous with "Will"
S + will have been + Ving
Examples:
• You will have been waiting for more than an hour when her plane finally arrives.
• Will you have been waiting for more than an hour when her plane finally arrives?
• You will not have been waiting for more than an hour when her plane finally arrives.

FORM Future Perfect Continuous with "Be Going To"
S + am/is/are + going to have been + present participle
Examples:
• You are going to have been waiting for more than an hour when her bus finally arrives.
• Are you going to have been waiting for more than an hour when her bus finally arrives?
• You are not going to have been waiting for more than an hour when her bus finally arrives.

NOTE: It is possible to use either "will" or "be going to" to create the Future Perfect Continuous with little or no difference in meaning.

We use the Future Perfect Continuous to show that something will continue up until a particular event or time in the future. "For five minutes," "for two weeks," and "since Friday" are all durations which can be used with the Future Perfect Continuous. Notice that this is related to the Present Perfect Continuous and the Past Perfect Continuous; however, with Future Perfect Continuous, the duration stops at or before a reference point in the future.

Examples:

• We will have been talking for over an hour by the time Thomas arrives.
• She is going to have been working at that company for five years when it finally closes.
• James will have been studying at the university for more than a year by the time he leaves for Asia.
• How long will you have been studying when you graduate?

Notice in the examples above that the reference points (marked in italics) are in Simple Present rather than Simple Future. This is because these future events are in time clauses, and you cannot use future tenses in time clauses.
Using the Future Perfect Continuous before another action in the future is a good way to show cause and effect.

Examples:
• Jason will be so tired when he gets home because he will have been jogging for over an hour.
• John's English will be very good when she returns to Germany because she is going to have been studying English in the United States for over two years.