Future Perfect or Future Perfect Continuous
The future perfect is used to talk about things which will already have been completed by a specific time in the future.
To use the future perfect, we usually need to say what point in the future that is by using a phrase with ‘by…’:
by tomorrow / by next week / by next year etc.
By this time tomorrow I will have arrived in New York
The future perfect is used for quick single events which will have happened by a certain point in the past:
e.g. arriving in a new city (this only takes a second) / finishing a report (finishing only takes 1 second)
For continuing / longer / repeating events it is possible that we may need to use the future perfect continuous:
e.g. writing a report (this takes a long time) / calling your friend when they do not answer the phone (sometimes you call your friend many times with no answer)
but we do not use future perfect continuous all the time with continuing or repeating events, in fact we do not use it so often, but sometimes we MUST use it, see the image below to find when we need to use future perfect continuous for continuing or repeating events..
Beware also that there are some verbs which cannot be used in any of the continuous tenses. Some verbs will sound strange to you in the continuous form, and it is a good idea to learn what these verbs are: Verbs that Cannot be Used in the Continuous Tenses