Se eu estudar com calma durante todo o ano, passo a confiar mais em mim.

Because after se meaning if, Portuguese often uses the future subjunctive when the condition refers to a possible future situation.

So:

• Se eu estudar... = If I study / If I should study
• Se eu estudo... would not fit this meaning in standard Portuguese

In this sentence, the idea is: if, at some point in the future, I study calmly throughout the year...

It looks like an infinitive, but here it is actually the future subjunctive form.

For many regular verbs, the future subjunctive has the same form as the personal infinitive and the plain infinitive. That is why it can be confusing.

For estudar:

• infinitive: estudar
• future subjunctive, eu: estudar
• personal infinitive, eu: not normally used with eu in this way here

So in this sentence, se eu estudar is definitely a future subjunctive structure.

Passo is the present indicative of passar. In sentences like this, Portuguese often uses the present to express a general result, a habitual consequence, or something the speaker sees as a regular pattern.

So:

• Se eu estudar com calma durante todo o ano, passo a confiar mais em mim.

means something like:

• If I study calmly throughout the year, I start to trust myself more
• Whenever I do that, I become more self-confident

If you wanted a more explicitly future reading for a single future situation, passarei a confiar could also work, but the original sentence sounds more like a general truth or repeated effect.

Passar a + infinitive means to start to, to come to, or to begin to do something.

So:

• passo a confiar mais em mim = I start to trust myself more / I come to trust myself more

This structure often suggests a change of state:

• before: less trust
• after: more trust

It is very common in Portuguese.

Examples:

• Passei a gostar de café. = I started to like coffee.
• Ela passou a estudar mais. = She started studying more.

Because the expression is passar a + infinitive.

So the full pattern is:

• passar a fazer
• passar a sentir
• passar a confiar

In European Portuguese, this a + infinitive pattern is extremely common after many verbs and verbal expressions.

Here:

• passo a confiar = I start trusting / I come to trust

You cannot normally drop the a in this structure.

Because after a preposition such as em, Portuguese uses the stressed pronoun, not the subject pronoun.

So:

• subject pronoun: eu
• after a preposition: mim

That is why you say:

• em mim = in me / on myself
• not em eu

Other examples:

• para mim
• de mim
• sem mim

When confiar means to trust someone or something, it normally uses em:

• confiar em alguém = to trust someone
• confiar em si próprio = to trust oneself

So:

• confiar mais em mim = to trust myself more

Be careful, because confiar can also appear in a different structure when it means to entrust something to someone:

• Confiou-me um segredo. = He entrusted a secret to me.

But in your sentence, the meaning is clearly to trust, so em is the right preposition.

Com calma means something like:

• calmly
• without rushing
• at an unhurried pace
• carefully and steadily

In this sentence, it does not just describe emotion. It suggests a way of studying that is steady, relaxed, and not rushed.

So estudar com calma is often more natural than a literal English-style idea like study calmly.

Durante todo o ano means throughout the whole year or all year long.

Yes, it is very close in meaning to o ano todo.

Compare:

• durante todo o ano = throughout the whole year
• o ano todo = the whole year / all year

Both are natural. Durante todo o ano sounds a bit more explicit and structured. O ano todo can sound a little more conversational.

Because the sentence begins with a conditional clause:

• Se eu estudar com calma durante todo o ano, ...

When this kind of clause comes first, it is very common to separate it from the main clause with a comma.

So the structure is:

• conditional clause
  • comma + main clause

If you reverse the order, the comma is often not needed:

• Passo a confiar mais em mim se eu estudar com calma durante todo o ano.

Both are possible, but the original order is very natural.

Yes. Here se means if.

You can tell because it introduces a condition:

• If I study calmly throughout the year, I start to trust myself more.

When se means whether, it usually introduces an indirect yes/no question:

• Não sei se ele vem. = I don’t know whether he is coming.

That is not what is happening in your sentence.

Yes, you could, and it would be very close in meaning.

• começo a confiar mais em mim = I begin to trust myself more
• passo a confiar mais em mim = I come to trust myself more / I start trusting myself more

The difference is slight:

• começar a focuses more on the beginning
• passar a often emphasizes a change into a new state or habit

So passo a confiar mais em mim can sound a bit more like I become the kind of person who trusts myself more.

Yes, it is natural and correct in European Portuguese.

It sounds like a reflective, fairly standard sentence. A native speaker might also choose slightly different wording depending on style, for example:

• Se eu estudar com calma ao longo do ano, passo a confiar mais em mim.
• Se eu estudar com calma durante o ano todo, passo a confiar mais em mim.

But your original sentence is perfectly normal.