Future Perfect

The future perfect is a verb form or construction used to describe an event that is expected or planned to happen before a time of reference in the future (future tense), such as will have finished in the English sentence "I will have finished by tomorrow."

Future Perfect - Details events in the future

The main function of the future perfect tense is to indicate that something will have happened by a certain point in the future. It indicates completion of an action that has not reached completion yet. 

Structurally, the future perfect is constructed by just using the phrase "will have", followed by the past participle of the desired verb. The future perfect construction is actually thus pretty simple, once you get the hang of it.  

Using perfect tense in a sentence

For your reference, here is an example of the future perfect being used in a correct way. 

"By the time the next fiscal year will have arrived, the CEO promised that the company surely will have achieved its financial objectives." 

In this sentence, the future perfect is used correctly in both the phrase "will have arrived" and the phrase "will have achieved". 

Now, here is an example of the incorrect use of the future perfect.

"The author was concerned about the fact that by the time his book is published, he will have spended all his money."

The problem here is that the correct past participle of the verb "spend" is not "spended", but rather "spent". 

Here are a few simple rules to follow:

1. The future perfect construction itself is really very simple. The main thing you need to think about is simply whether this form is the appropriate one for the action or situation you're trying to convey. Again: the future perfect is used to describe an action that will have been completed by a certain time in the future. Otherwise, some other form should be used. 
2. The only potentially tricky thing about the future perfect is that the past participle of certain verbs may have irregular constructions. For example, the past participle of the verb sleep is not sleeped but rather slept. This may seem counterintuitive at first, and learning the proper past tense forms may just be a matter of practice and experience more than anything else.  

Further usage and examples

The main use of the future perfect construction is to help people talk about situations that people expect to exist in the future. For example, if one is worried about the fact that he will have spent all his money, then this using the future perfect to express this concern could potentially enable him to plan meaningful actions to address the concern. If the future perfect scenario is desirable, then a person can continue to do what he is doing; or if it is undesirable, then he can change what he is doing, in order to make sure the scenario doesn't come about. 

As such, it is clear that the future perfect may come in very hand within disciplines such as business or management, where people are consciously attempting to make a certain kind of future scenario come about. The future perfect provides people with the grammatical tools they will need to talk about these concerns in a meaningful way. Likewise, a scientist may say that within two weeks from now, he will have discovered whether his hypothesis is true or false. The future perfect is thus highly useful when one wants to talk about projected objectives.