1: Just like with the other perfect continuous tenses (and
the future
perfect simple), we can use the future perfect continuous to say 'how long'
for an action that continues up to another point in the future. The second
point can be a time or another action. Generally, we need 'for + length of
time' and if we use 'when' or 'by the time', we usually use the present
simple.
In April, she will have been teaching for twelve years.
By the time you arrive, I'll have been cooking for hours!
In the same way as with the future
perfect simple, we often use the future perfect continuous because we like
easy numbers. It's also possible to use the present perfect continuous, but
then we get a more complicated number.
I've been working here for 11 months and three weeks. (This
is correct, but the time is not an easy number.)
On Tuesday, I will have been working here for one year. (A
much easier number.)
2: We can use the future perfect continuous, like the other
perfect continuous tenses, to talk about something that finishes just before
another time or action (in this case, in the future). It's often used because
there will be a result at the second point in the future. (Again, if we use
'when' we usually need the present
simple.)
When I see you, I'll have been studying, so I'll be tired.
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