Segundo o banco, os juros rotativos vão mudar.

In Portuguese, segundo can mean two different things:

• second as an ordinal number: o segundo capítulo = the second chapter
• according to as a preposition: Segundo o banco... = According to the bank...

In your sentence, it is clearly the second meaning because it is followed by a noun phrase, o banco, and introduces a source of information.

A very similar English pattern would be:

• According to the bank, ...

So here segundo is not about numbers at all.

Because Segundo o banco is an introductory phrase that tells you the source of the statement.

So the sentence is structured like this:

• Segundo o banco, = According to the bank,
• os juros rotativos vão mudar. = the revolving interest charges are going to change.

The comma helps separate that introductory source phrase from the main statement. In Portuguese, this kind of comma is very common and natural.

Here, banco means bank in the financial sense.

Portuguese banco can also mean bench, depending on context, but in this sentence the financial meaning is the obvious one because the rest of the sentence talks about juros = interest.

So:

• o banco = the bank

Portuguese uses articles much more often than English does.

So where English might sometimes say:

• According to banks...
• According to the bank...

Portuguese often prefers an article:

• Segundo o banco... = according to the bank
• Segundo os bancos... = according to the banks

Here o banco suggests a specific bank, or a bank already understood from context.

Using no article here would sound unnatural in normal Portuguese.

Juros means interest in the financial sense.

A very important point for English speakers: Portuguese usually uses juros in the plural where English often uses singular interest.

Examples:

• pagar juros = to pay interest
• taxa de juros = interest rate
• juros altos = high interest

There is also a singular form, juro, but in everyday financial language juros is much more common.

That is why the sentence has plural agreement later:

• os juros rotativos vão mudar
• not vai mudar

In Brazilian Portuguese, juros rotativos usually refers to the interest charged in crédito rotativo, especially the revolving balance on a credit card.

So this is not just any kind of interest. It is a specific financial category: interest on a balance that keeps rolling over instead of being fully paid.

Breaking it down:

• juros = interest
• rotativos = revolving / rolling over

Together, it means something like:

• revolving interest
• interest on revolving credit
• in many contexts, specifically credit card revolving interest

Because it agrees with juros, which is masculine plural.

Agreement in Portuguese works like this:

• juro rotativo = singular
• juros rotativos = plural

So:

• juros = plural
• rotativos = also plural

This is standard adjective agreement.

Because the subject is os juros rotativos, which is plural.

The verb ir in vão mudar must agree with the subject:

• o juro vai mudar = the interest charge is going to change
• os juros vão mudar = the interest charges are going to change

So vão is plural because juros is plural.

Both are possible, but ir + infinitive is extremely common in Brazilian Portuguese.

So:

• vão mudar = are going to change
• mudarão = will change

In modern Brazilian Portuguese, vão mudar often sounds more natural and common, especially in speech and everyday writing.

This is very similar to English, where people often prefer are going to change instead of will change.

Not in this sentence.

The verb ir normally means to go, but when it is followed by an infinitive, it often forms a future expression:

• vou estudar = I am going to study
• eles vão chegar = they are going to arrive
• os juros vão mudar = the interest charges are going to change

So here vão mudar is a future construction, not physical movement.

Here mudar means to change or to undergo change.

So os juros rotativos vão mudar means the rates/charges themselves will change.

If you wanted to say they will be changed by someone, Portuguese would often use a passive structure, such as:

• Os juros rotativos serão alterados
• Os juros rotativos serão mudados is possible grammatically, but less natural in many financial contexts

In this sentence, mudar is being used in the intransitive sense: the thing itself changes.

Yes. Portuguese allows some flexibility.

For example:

• Os juros rotativos vão mudar, segundo o banco.

This still means the same thing: According to the bank, the revolving interest charges are going to change.

The original version puts the source first:

• Segundo o banco, ...

That makes the source sound immediately important.

Yes. That would be very natural.

Examples:

• Segundo o banco, os juros rotativos vão mudar.
• De acordo com o banco, os juros rotativos vão mudar.
• Conforme o banco, os juros rotativos vão mudar.

All of these can mean according to the bank.

Nuance:

• segundo is concise and common in news-style language
• de acordo com is very common and neutral
• conforme can sound slightly more formal or written, depending on context

It sounds mostly neutral, with a slightly news/business tone.

Reasons:

• Segundo o banco is a very common way to report information
• juros rotativos is financial vocabulary
• vão mudar keeps it natural and modern, especially in Brazilian Portuguese

So it would fit well in journalism, financial news, or everyday discussion about banking.