A taxa de juro é baixa.

Because de juro is a fixed expression meaning of interest / interest-related.

In Portuguese, taxa de juro is the normal way to say interest rate. Here, de links the two nouns in a general way, similar to rate of interest.

• taxa = rate
• juro = interest

You normally say:

• taxa de juro = interest rate
• taxas de juro = interest rates

Using do juro would usually sound too specific here, as if you meant the rate of the interest in a particular, unusual context.

In European Portuguese, taxa de juro in the singular is a very common standard expression.

So:

• a taxa de juro = the interest rate
• as taxas de juro = the interest rates

You may also come across juros in other contexts, because juros is very common when talking about interest as money charged or earned:

• pagar juros = to pay interest
• os juros são altos = the interest is high

But in the set phrase taxa de juro, the singular juro is normal.

Portuguese usually uses the definite article more often than English.

So A taxa de juro é baixa literally starts with The interest rate... Even when English might say just interest rates are low or the interest rate is low, Portuguese often prefers an article.

Here:

• a = the for a feminine singular noun
• taxa is feminine singular

So a taxa is grammatically natural and expected.

Because adjectives normally agree with the noun they describe.

The noun here is taxa, which is:

• feminine
• singular

So the adjective must also be feminine singular:

• baixo = masculine singular
• baixa = feminine singular
• baixos = masculine plural
• baixas = feminine plural

That is why we say:

• A taxa de juro é baixa.

If the noun were masculine, you would use baixo instead.

É is the he/she/it is form of the verb ser.

The sentence is describing a quality of the interest rate: it is low. For general descriptions and definitions, Portuguese often uses ser, just as English uses to be.

So:

• A taxa de juro = the interest rate
• é = is
• baixa = low

Together: The interest rate is low.

Yes, you might hear that, but é baixa and está baixa are not exactly the same.

• é baixa suggests a more general or inherent description: the rate is low.
• está baixa suggests a current state or temporary condition: the rate is low at the moment.

In many real contexts, both are possible, but é baixa is a very natural neutral statement.

Here, baixa means low.

It agrees with taxa, so it is the feminine form of baixo.

Examples:

• preço baixo = low price
• temperatura baixa = low temperature
• taxa baixa = low rate

Be careful: baixo/baixa can also mean short or low/down in other contexts, depending on what it describes.

The word order is very straightforward and matches a common English pattern:

• A taxa de juro = subject
• é = verb
• baixa = adjective / complement

So it is basically:

[subject] + [verb] + [adjective]

This is the most neutral and natural order.

You would change the article, noun, verb, and adjective as needed:

• As taxas de juro são baixas.

Breakdown:

• A → As
• taxa → taxas
• é → são
• baixa → baixas

Notice that juro usually stays singular in this expression even after taxas:

• taxas de juro

A careful European Portuguese pronunciation would be approximately:

a TAX-a d(e) JU-ro é BAI-sha

A few useful notes:

• taxa sounds roughly like TA-sha
• de is often reduced in speech
• juro begins with the Portuguese j sound, like the s in measure
• baixa sounds roughly like BAI-sha

European Portuguese often reduces unstressed vowels more than Brazilian Portuguese, so some sounds may be less clear than their spelling suggests.

It is neutral and perfectly standard.

You could use it in:

• news reports
• economics discussions
• banking contexts
• everyday conversation

It is not slangy or overly formal. It is a normal, correct sentence in European Portuguese.