Compound tenses are formed by an auxiliary verb and a participle. In Portuguese, the most common auxiliary is "ter" and, in formal or registry contexts, "haver" is also used. The participle carries the main meaning of the action, while the auxiliary marks tense, mood, person, and number. Compound tenses express anteriority relative to another time or reference point.

The basic structure is a conjugated auxiliary + invariable participle. The auxiliary is conjugated according to the chosen tense and mood. The participle remains the same for all persons, except in adjectival or passive constructions, which are not part of standard compound tenses. The choice between "ter" and "haver" may depend on register and variety, but the syntactic formation is equivalent.

The participle is the form used in compound tenses to express the result or completion of the action. For regular verbs, it is formed with -ado for the first conjugation and -ido for the second and third. Irregular verbs may have their own participles that must be memorized. In compound tenses, the short participle is used, not the extended or periphrastic participle.

The present perfect compound expresses an action repeated or habitual that began in the past and continues to the present, with focus on the continuity of the result. It is formed by "ter" in the present indicative plus the participle. It does not equate to the simple past in English or to the simple past in Portuguese, because it implies repetition or continuity. It is common in situations where one wants to indicate frequency or persistence up to now.

The past perfect compound expresses an action prior to another past action. It is formed by "ter" in the imperfect indicative plus the participle. It serves to establish a temporal sequence in the past, marking anteriority. It is widely used in spoken and written language as an alternative to the simple pluperfect.

The future perfect indicates an action that will be completed before a future point or before another future action. It is formed by "ter" in the future indicative plus the participle. It tends to appear in planned contexts, forecasts with anteriority or instructions. In formal language, it may appear with "haver" instead of "ter".

In the subjunctive, compound tenses express anteriority relative to a hypothetical or dependent reference point. The present perfect subjunctive uses "ter" in the present subjunctive plus the participle and is often equivalent to having already done in dependent contexts. The past perfect subjunctive compound uses "ter" in the imperfect subjunctive plus the participle and marks hypothetical anteriority in the past. The choice depends on the temporal relationship within the complex clause.

"Ter" is the predominant auxiliary in compound tenses of contemporary Portuguese, especially in speech and informal writing. "Haver" appears more in formal, legal, or academic registers, maintaining equivalent meaning. The choice may vary by region and stylistic tradition, but it does not alter the basic structure of the compound tense. In many contexts, the alternation of "ter" and "haver" is a matter of style and not of temporal grammar.

Compound tenses combine a conjugated auxiliary and a participle to express anteriority. The present perfect compound indicates repetition or continuity up to the present. The past perfect compound marks anteriority relative to another past. The future perfect indicates completeness before a future point, and the subjunctive compound tenses place anteriority in dependent contexts.