A taxa de juro baixou, de modo que poupei.

Because taxa is a specific, countable noun here, so Portuguese normally uses the definite article: a taxa de juro = the interest rate.

In Portuguese, articles are often used more than in English. So where English might sometimes say interest rates fell, Portuguese often prefers a taxa de juro baixou when talking about a specific rate in context.

De juro means of interest or interest-related. So taxa de juro is the standard way to say interest rate.

This is a common Portuguese structure:

• taxa de juro = interest rate
• taxa de câmbio = exchange rate
• taxa de inflação = inflation rate

So de links the main noun to the thing that defines it.

In this expression, Portuguese normally says taxa de juro in the singular. Even though English often uses interest as an uncountable noun, Portuguese uses juro here as part of a fixed expression.

You may also see taxa de juros in Brazilian Portuguese, but taxa de juro is the standard European Portuguese form.

Baixou is the pretérito perfeito (simple past) of baixar.

Here it means went down / fell / dropped in a completed way:

• baixar = to go down, to lower, to decrease
• baixou = it went down / it fell

So A taxa de juro baixou means the rate fell at a particular point or over a finished period.

Because the subject is singular: a taxa.

The full subject is a taxa de juro, and the head noun is taxa, which is singular and feminine. The verb agrees with taxa, not with juro.

So:

• A taxa de juro baixou = singular
• As taxas de juro baixaram = plural

De modo que means so, so that, or in such a way that, depending on context.

In this sentence, it introduces a consequence:

• A taxa de juro baixou, de modo que poupei.
• The rate fell, so I saved.

It is a bit more formal or written than simply por isso or por isso mesmo. In everyday speech, many people might prefer:

• A taxa de juro baixou, por isso poupei.

Not always. It can introduce either:

1. consequence: so, therefore
2. purpose/manner in some contexts: so that, in such a way that

In your sentence, it clearly expresses consequence:

• the rate went down
• as a result, I saved

So here it is best understood as so or with the result that.

Because de modo que introduces a second clause explaining the result of the first one. In Portuguese, it is normal to separate this kind of connector with a comma.

So the structure is:

• main clause: A taxa de juro baixou
• result clause: de modo que poupei

The comma helps show the logical pause and relationship between the two ideas.

Poupei is also pretérito perfeito, from the verb poupar.

It means I saved in a completed sense.

So the sentence has two completed actions/events:

• baixou = it fell
• poupei = I saved

This matches the idea that one event led to another.

It can mean either, depending on context.

The verb poupar can mean:

• to save money
• to economise
• sometimes to spare

In this sentence, because it follows the interest rate fell, poupei most naturally means I saved money or I paid less / spent less than before.

Because Portuguese often leaves out subject pronouns when the verb ending already shows who the subject is.

Poupei clearly means I saved, so eu is not necessary.

You could say:

• ... de modo que poupei.
• ... de modo que eu poupei.

But the version without eu is more neutral and more natural unless you want emphasis or contrast.

Yes, but it adds emphasis.

• ... de modo que poupei. = neutral
• ... de modo que eu poupei. = I saved (perhaps not someone else, or with extra emphasis)

Portuguese often omits subject pronouns unless there is a reason to stress them.

Here it is intransitive.

• A taxa de juro baixou = the interest rate fell

No direct object is needed. The subject itself undergoes the change.

But baixar can also be transitive in other contexts:

• O governo baixou os impostos. = The government lowered taxes.

So baixar can mean either to go down or to lower something, depending on the structure.

Sometimes, but baixou is more natural here.

Both baixar and descer can involve the idea of going down, but with rates, prices, and levels, baixar is usually the more idiomatic choice:

• A taxa de juro baixou = natural
• A taxa de juro desceu = understandable, but less standard in this context

For economic figures, baixar is generally safer.

If you are learning European Portuguese, it is better to use A taxa de juro baixou.

Taxa de juros is much more associated with Brazilian Portuguese. In Portugal, the standard form is taxa de juro.

So for Portugal Portuguese:

• preferred: taxa de juro

It is mostly neutral to slightly formal.

The reason is de modo que, which sounds a bit more written or careful than everyday conversational connectors like:

• por isso
• então

So:

• A taxa de juro baixou, de modo que poupei. = correct, a bit formal/written
• A taxa de juro baixou, por isso poupei. = more everyday

Not by itself. Poupei simply means I saved.

If you wanted the idea of managed to save, Portuguese would usually make that clearer:

• consegui poupar
• consegui economizar in Brazilian Portuguese

So poupei on its own does not necessarily imply effort or difficulty; it just states the result.

In this sentence, no. Here de modo que expresses a real consequence, so the indicative is used:

• de modo que poupei

When expressions like de modo que or similar connectors express purpose rather than result, Portuguese can use the subjunctive in other contexts. But here the meaning is factual: the rate fell, and as a result, I saved.

So poupei is correctly in the indicative.