The future perfect tense is used to describe an event that has not yet happened but is expected or planned to happen before another stated occurrence.

Formation of the future perfect in English

In English, this tense is formed as such:

subject + shall or will have + past participle of verb = "I shall have gone to the store by the time you come." In linguistics, a participle is a kind of verbal adjective; it indicates that the noun it modifies is a participant in the action that the participle refers to. ... A verb is a part of speech that usually denotes action (bring, read), occurrence (to decompose (itself), to glitter), or a state of being (exist, live, soak, stand). Depending on the language, a verb may vary in form according to many factors, possibly including its tense, aspect, mood and voice. ...

This is usually shortened with the contraction of 'll for shall or will: I'll have been hit, you'll have been paid, etc. To make this form negative, one simply adds "not" between "will" or "shall" and "have." For the contracted form: I won't have been speaking, you won't have been speaking, etc. In traditional grammar, a contraction is the formation of a new word from two or more individual words. ...

In legal writing, the future perfect often appears by way of the phrase "shall be" or "shall have been," with the general result of obscuring, rather than enhancing, the writer's meaning.

Spanish future perfect

In Spanish, the future perfect is formed as such:

subject + future form of haber (auxiliary verb) + past participle = yo habré hablado (I will have spoken). In linguistics, an auxiliary (also called helping verb, auxiliary verb, or verbal auxiliary) is a verb functioning to give further semantic or syntactic information about the main or full verb following it. ...

The future of haber is formed by the future stem "habr" + the endings -é, -ás, -á, -emos, -éis, -án. The past participle of a verb is formed by adding the endings -ado and -ido to ar and er/ir verbs, respectively. However, there are a few irregular participles, some of the more common ones listed here:

abrir: abierto
cubrir: cubierto
decir: dicho
escribir: escrito
freír: frito
hacer: hecho
morir: muerto
poner: puesto
ver: visto
vovler: vuelto

Be aware that verbs within verbs also have the same participle, for example, predecir (to predict) would be predicho; suponer (to suppose) would be supuesto. Also, satisfacer (to satisfy) is close to hacer (to do) in that the past participle is satisfecho.

To make the tense negative, one simply adds "no" before the form of haber: yo no habré hablado. For use with reflexive verbs, one puts the reflexive pronoun before the form of haber: from bañarse (to take a bath), yo me habré bañado; negative: yo no me habré bañado. In grammar, a reflexive verb is a verb whose semantic agent and patient (typically represented syntactically by the subject and the direct object) are the same. ...

French future perfect

The French future perfect, called futur antérieur, is formed similarly to Spanish:

subject + auxiliary verb (avoir or être) + past participle = j'aurai parlé (I will have spoken).

Verbs that use être in the past ("House of Etre" verbs, reflexive verbs) also use être in forming the present perfect. For example, "je serai venu(e)" uses the future of être because of the action verb, venir (to come), which uses être in the past.

To form the future form of the auxiliary verbs, one uses the future stem and adds the endings -ai, -as, -a, -ons, -ez, -ont. Both avoir and être have irregular future stems; while, with the exception of -re verbs, most verbs use the infinitive as the future stem (i.e. je parlerai, I will speak), the future stem of avoir is "aur," and that of être is "ser."

To form the past participle in French, one usually adds -é, -i, and -u to the roots of -er, -ir, and -re verbs, respectively. However, there are many exceptions to this rule, including these commonly used ones (and all of their related verbs):

faire: fait
mettre: mis
ouvrir: ouvert prendre: pris
venir: venu

Verbs related to mettre (to put): promettre (to promise); to ouvrir: offrir (to offer), souffrir (to suffer); to prendre (to take): apprendre (to learn), comprendre (to understand); to venir (to come): revenir (to come again), devenir (to become).

When using être as the auxiliary verb, make sure that the past participle agrees with the subject: je serai venu (I [masc.] will have come), je serai venue (I [fem.] will have come); nous serons venus (We [masc. or mixed] will have come), nous serons venues (We [fem.] will have come). Verbs using avoir do not need agreement.

To make this form negative, one simply adds "ne" (n' if before vowel) before the auxiliary verb and "pas" after it: je n'aurai pas parlé; je ne serai pas venu. For reflexive verbs, one puts the reflexive pronoun before the auxiliary verb: from "se baigner" (to take a bath), je me serai baigné; negative: je ne me serai pas baigné.

In German

To form the future perfect tense in German, you use the auxiliary verb werden (as in the perfect tense, and then put the past participle followed by its auxiliary verb (sein or haben) in the infinitive. This literally takes the perfect tense formation and puts it into the future. For example:

 Ich werde etwas geschrieben haben. I will something written have. I will have written something. 

In Dutch

The dutch future tense is very similar to the German future tense in many ways. It is formed by using the verb zullen (shall), then placing the past participle and after that, hebben (to have) is put after it. Example:

 Ik zal iets geschreven hebben. I shall something written have. I will have something written. Wir werden maths morger haben. we will maths tomorrow have. we will have maths tomorrow. 

In Latin

The future perfect is found by using the perfect stem + a declined future being verb (ero). An exception is that the active indicative 3rd person plural is formed from the perfect stem + erint, instead of + erunt. E.g., amaverint, not amaverunt.

The passive is the perfect passive participle and ero.

 Amavero Amatus ero Putavero Putatus ero 

Use of the future perfect

The future perfect tense is used to say that something will happen in the future, but before the time of the main sentence. It is most often used in the construction "When/By the time something has occurred, I will have done something."