O rendimento isento não muda o imposto devido.

Not exactly.

• rendimento often means income, earnings, return, yield, proceeds
• renda often means income in a broader, more everyday sense

In financial, tax, or administrative language, rendimento is very common for specific kinds of income or earnings, especially when talking about salaries, investments, bank income, taxable amounts, and so on.

So in this sentence, o rendimento isento is something like the exempt income / tax-exempt earnings.

In Portuguese, adjectives often come after the noun.

So:

• rendimento isento = exempt income
• imposto devido = tax due / tax owed

English often puts adjectives before the noun, but Portuguese very often places them after it.

You can sometimes move adjectives before the noun in Portuguese, but that usually changes the tone or emphasis. In this sentence, the normal and natural order is rendimento isento.

Here, isento means exempt — specifically exempt from tax.

So rendimento isento means income that is not subject to taxation.

Be aware that isento can also mean impartial or unbiased in other contexts, but that is not the meaning here.

Portuguese uses definite articles much more often than English.

So:

• o rendimento isento
• o imposto devido

Even when English might say something more general like exempt income or tax due, Portuguese commonly uses the article.

This is very normal and does not necessarily make the sentence sound more specific than in English.

Because the subject is singular: o rendimento isento.

Breakdown:

• o rendimento isento = singular subject
• muda = 3rd person singular of mudar

So the sentence literally follows this pattern:

• [singular subject] + não + [singular verb]

If the subject were plural, the verb would also be plural:

• Os rendimentos isentos não mudam o imposto devido.

That is the normal way to make a sentence negative in Portuguese.

Pattern:

• não + verb

So:

• não muda = does not change

This is much more straightforward than English, because Portuguese does not need do/does/did support in this kind of sentence.

Compare:

• muda = changes
• não muda = does not change

Here, devido means due or owed.

So:

• o imposto devido = the tax due
• or more naturally, the tax owed

It is describing the noun imposto, just like isento describes rendimento.

Yes.

devido is historically the past participle of dever (to owe / must), but in this sentence it is functioning as an adjective.

So:

• dever = to owe
• devido = due, owed

This is very common in formal and financial Portuguese.

Also remember agreement:

• imposto devido = masculine singular
• taxa devida = feminine singular
• valores devidos = masculine plural
• quantias devidas = feminine plural

Yes, depending on context.

The basic meaning of mudar is to change. But in a sentence like this, natural English might sometimes prefer:

• does not change
• does not affect
• does not alter

In Portuguese, a more formal alternative might be:

• O rendimento isento não altera o imposto devido.

That sounds slightly more technical or formal, but the original sentence with muda is perfectly understandable.

It sounds neutral to somewhat formal, mainly because of the tax/financial vocabulary:

• rendimento
• isento
• imposto devido

This is the kind of sentence you might see in:

• a tax form
• a financial explanation
• banking or accounting material
• government guidance

In casual conversation, people might choose simpler wording depending on the context, but this sentence itself is natural for administrative or financial Portuguese.

Yes, rendimento isento de imposto would also be correct and more explicit.

Compare:

• rendimento isento = exempt income
• rendimento isento de imposto = income exempt from tax

The shorter version works because the tax context is already clear. Portuguese often leaves out information that is easy to infer from context.

Yes.

Portuguese adjectives usually agree in gender and number with the nouns they describe.

Here:

• rendimento is masculine singular → isento
• imposto is masculine singular → devido

If the nouns changed, the adjectives would change too:

• a renda isenta
• as rendas isentas
• os impostos devidos

This agreement is an important feature of Portuguese grammar and something English speakers often need to get used to.