Em janeiro, eu sempre compro um calendário novo e escrevo as datas importantes.

With months in Portuguese, em is the normal preposition:

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

You usually do not use an article before the month here, so no janeiro sounds wrong in this sentence.

A useful pattern is:

• em + month
• em janeiro
• em março
• em dezembro

Em janeiro is a time expression placed at the beginning of the sentence. In Portuguese, it is very common to separate that kind of introductory phrase with a comma.

So:

• Em janeiro, eu sempre compro...

This is similar to English writing:

• In January, I always buy...

The comma is natural and standard here.

Not always. Portuguese often drops subject pronouns when the verb form already makes the subject clear.

So both of these are possible:

• Em janeiro, eu sempre compro...
• Em janeiro, sempre compro...

Because compro already means I buy, eu is optional.

Why include eu, then?

• for emphasis
• for clarity
• for a slightly more explicit style

In everyday Brazilian Portuguese, omitting eu is very common.

They are in the present indicative because the sentence describes a habit or something the speaker regularly does.

The word sempre helps show that this is habitual:

• eu sempre compro
• escrevo

So this present tense is not just right now present. It can also mean:

• something you do regularly
• a routine
• a general habit

That is very common in Portuguese, just as in English: I always buy... and write...

The ending -o marks the first person singular: I.

Examples:

• comprar → compro = I buy
• escrever → escrevo = I write

So in this sentence:

• eu compro = I buy
• eu escrevo = I write

This is why Portuguese often does not need the pronoun eu: the verb ending already tells you who is doing the action.

In Portuguese, adverbs like sempre often come before the main verb:

• eu sempre compro
• ela sempre chega cedo

That is the most neutral and natural placement here.

You may also hear different placements in some contexts, but eu sempre compro is the standard choice learners should use first.

Both are possible, but they can sound slightly different.

• um calendário novo usually means a calendar that is new in the ordinary sense
• um novo calendário can suggest a new/different calendar, often with a bit more emphasis on it being another one

In everyday Portuguese, putting the adjective after the noun is very common:

• carro novo
• livro interessante
• datas importantes

So um calendário novo is the most straightforward and natural phrasing here.

Portuguese uses definite articles more often than English.

So as datas importantes means something like:

• the important dates

Here, the speaker is referring to a specific set of dates they consider important, so the article sounds natural.

You could sometimes hear datas importantes without as, but that would sound more general or less specific. In this sentence, as datas importantes is the most natural choice.

Because the adjective must agree with the noun.

Here:

• datas is feminine plural
• so the adjective must also be plural: importantes

Agreement in Portuguese usually works like this:

• data importante = singular
• datas importantes = plural

Notice that importante has the same form for masculine and feminine in the singular, but it still changes for number:

• importante
• importantes

No. In this sentence, data means date.

This is an important false friend for English speakers:

• data = date
• dados = data / information / data points

So:

• as datas importantes = the important dates

not the important data.

Because the same subject continues across both verbs.

The structure is:

• eu sempre compro um calendário novo
• e escrevo as datas importantes

The subject eu applies to both compro and escrevo, so it does not need to be repeated.

You could say:

• eu sempre compro um calendário novo e eu escrevo as datas importantes

but that sounds more repetitive and less natural unless you want emphasis.

Yes. In this context, escrever as datas importantes usually means writing down or marking the important dates in the calendar.

Portuguese often uses escrever in a simple, natural way for this idea. Depending on context, speakers might also say things like:

• anoto as datas importantes = I write down / note the important dates
• marco as datas importantes = I mark the important dates

But escrevo as datas importantes is perfectly correct and easy to understand.