Em maio, eu costumo rever cada ficha antes da avaliação final.

Portuguese uses em with months, so em maio means in May.

• em janeiro = in January
• em fevereiro = in February
• em maio = in May

In everyday Portuguese, em + o/a can contract to no/na, but that does not happen with month names here. So no maio is not correct.

In Portuguese, the names of months are normally written with a lowercase letter, unlike in English.

So:

• maio = correct
• Maio = usually not standard unless it starts a sentence or appears in a title

The same is true for days of the week and seasons in standard Portuguese spelling.

Not really. Portuguese often drops the subject pronoun when the verb form already makes the subject clear.

So both are possible:

• Em maio, eu costumo rever cada ficha...
• Em maio, costumo rever cada ficha...

Both mean the same thing. Including eu can add a little emphasis or clarity, but it is not required.

Costumar + infinitive is a very common way to talk about habits or things you usually do.

So:

• costumo rever = I usually review / I tend to review

Examples:

• Costumo estudar à noite. = I usually study at night.
• Ela costuma chegar cedo. = She usually arrives early.

In your sentence, eu costumo rever means this is a regular habit in May.

Because the present tense in Portuguese can express a habitual action, just like in English with I usually...

So costumo does not mean only right now. It means something like:

• I usually do this
• I tend to do this
• This is my habit

Em maio gives the time frame, and costumo shows that it is a repeated or typical action during that time.

Rever means to review, to go over again, or sometimes to see again. It is built from ver = to see.

In a study context:

• ver = to see / look at
• rever = to review

So rever cada ficha means reviewing each worksheet/card/sheet, not just looking at it for the first time.

Yes, it follows the pattern of ver, so some forms are irregular.

For example:

• infinitive: rever
• eu revejo
• tu revês
• ele/ela revê
• nós revemos
• vocês revêm

In your sentence, the verb after costumo stays in the infinitive: costumo rever.

Cada means each or every, and it is followed by a singular noun:

• cada ficha = each worksheet / each card / each study sheet

A ficha can mean different things depending on context, especially in European Portuguese:

• worksheet
• record card
• file/card
• study sheet
• exercise sheet

So the exact English translation depends on the situation, but grammatically cada + singular noun is the key pattern.

Both are possible, but they are slightly different in feel.

• cada ficha focuses on the items one by one: each worksheet
• todas as fichas means all the worksheets as a group

So rever cada ficha suggests going through them individually, one by one. That often sounds very natural in study-related contexts.

Because antes de means before, and when de is followed by the feminine singular article a, they contract:

• de + a = da

So:

• antes de a avaliação final → antes da avaliação final

This is a very common contraction in Portuguese.

Portuguese often uses the definite article where English may or may not use one.

Here, a avaliação final refers to a specific final assessment, so the article is natural:

• antes da avaliação final = before the final assessment/exam

Without the article, the phrase would sound less natural in this context.

They are similar, but not always identical.

• avaliação final = final assessment/evaluation
• exame final = final exam

Avaliação is broader and can include different forms of assessment, not just one exam. In some contexts, it may still refer to a test, but exame is more specifically an exam.

Because Em maio is an introductory time expression. The comma helps separate that opening time phrase from the main part of the sentence.

So:

• Em maio, eu costumo rever...

This is natural and clear in writing. In short sentences, the comma may sometimes be omitted, but using it here is perfectly normal.

Yes. Portuguese allows some flexibility.

For example:

• Em maio, eu costumo rever cada ficha antes da avaliação final.
• Eu costumo rever cada ficha antes da avaliação final em maio.

But the first version is usually better if you want to emphasize the time frame in May from the beginning. The second can sound as if em maio is added later or may attach less clearly.

Yes, it fits European Portuguese very naturally, especially because ficha is very common in educational contexts in Portugal.

A learner should also know that in European Portuguese:

• subject pronouns like eu are often omitted unless needed
• vocabulary such as ficha is very common in school and study contexts

So the sentence sounds natural for Portugal, both grammatically and in vocabulary choice.