Cobraram uma comissão bancária, de modo que o saldo baixou.

In Portuguese, the subject is often left unstated when it is obvious, unknown, or simply not important.

Here, cobraram is 3rd person plural and works a bit like an indefinite they charged in English. It usually implies that some institution or people did it, and in this context that would most naturally be the bank.

So:

Cobraram uma comissão bancária
= They charged a bank fee / A bank fee was charged

A more explicit version would be:

O banco cobrou uma comissão bancária.

Using the unstated subject sounds very natural.

Both cobraram and baixou are in the pretérito perfeito simples, which is the normal past tense for completed actions/events.

• cobraram = they charged
• baixou = it went down / it decreased

This tense is used because the sentence describes completed events in the past:

1. the fee was charged
2. as a result, the balance went down

So the sentence presents a finished sequence of events.

In this sentence, comissão bancária means a bank fee, bank charge, or service fee.

Although comissão can sometimes correspond to English commission, in banking contexts it often refers to a fee charged by the bank. So a more natural English translation is often bank fee rather than bank commission.

For a learner, this is worth remembering because the most literal translation is not always the most natural one.

Portuguese normally uses an article here because it is referring to a particular fee event, even if the exact fee is not being identified in detail.

So:

cobraram uma comissão bancária
= they charged a bank fee

If you removed uma, the sentence would sound unnatural in normal Portuguese.

Compare:

• Cobraram uma comissão bancária. = They charged a bank fee.
• Cobraram a comissão bancária. = They charged the bank fee.
  This would mean a specific fee already known in the conversation.

De modo que means so, therefore, with the result that, or as a result.

In this sentence, it introduces the consequence of the first action:

Cobraram uma comissão bancária, de modo que o saldo baixou.
= They charged a bank fee, so the balance went down.

It is a correct and fairly natural connector, but it can sound a little more formal or written than very everyday options like:

• por isso
• por isso é que
• então (depending on context)

A more conversational version might be:

Cobraram uma comissão bancária, por isso o saldo baixou.

Here, que is part of the fixed connector de modo que.

You do not translate it word by word as a separate that in a very literal way. Instead, the whole expression functions as a linking phrase meaning so / with the result that.

So it is best to learn de modo que as one unit.

Yes. Baixar can be used intransitively to mean to go down, to drop, or to decrease.

So:

o saldo baixou
= the balance went down
= the balance decreased

This is a normal use.

The verb baixar can also be transitive in other contexts, meaning to lower something. But here it is intransitive: the balance itself decreased.

Other possible verbs would be:

• o saldo diminuiu
• o saldo reduziu-se

But baixou is very natural and idiomatic.

Yes. O saldo diminuiu is also correct and natural.

The difference is mostly one of style and wording:

• o saldo baixou = the balance went down
• o saldo diminuiu = the balance decreased

Baixar often feels a bit more direct and concrete, especially when talking about numbers, prices, levels, balances, and similar things.

Yes. In banking or financial context, saldo by itself very often means account balance.

So o saldo baixou is perfectly natural if the context already makes it clear that you are talking about a bank account or similar balance.

If you wanted to be more explicit, you could say:

o saldo da conta baixou

But it is not necessary here.

Yes, that is also correct.

Foi cobrada uma comissão bancária is a passive construction and means:

A bank fee was charged

Compared with Cobraram uma comissão bancária, the passive version sounds a bit more impersonal and often a bit more formal.

So both are possible:

• Cobraram uma comissão bancária = They charged a bank fee.
• Foi cobrada uma comissão bancária = A bank fee was charged.

Portuguese often prefers the active form with an omitted subject, especially in everyday language.

It is correct and natural, but it leans slightly toward a neutral-to-written style because of de modo que.

The first half, Cobraram uma comissão bancária, is very normal everyday Portuguese.

The connector de modo que is fine, but in casual speech many speakers would more often use something like:

Cobraram uma comissão bancária, por isso o saldo baixou.

So the sentence is not overly formal, but it is a little more polished than the most conversational version.

Yes. A very common rephrasing would be:

O saldo baixou porque cobraram uma comissão bancária.

This changes the structure from cause, then result to result, then cause:

• Cobraram uma comissão bancária, de modo que o saldo baixou.
• O saldo baixou porque cobraram uma comissão bancária.

Both are correct. The second version may feel simpler and more direct to many learners because porque is very familiar.