La retención reduce la cuota diferencial.

Because there are two separate noun phrases:

• la retención = the subject
• la cuota diferencial = the direct object

In Spanish, each noun normally takes its own article if it is definite. So this is completely normal:

• La retención reduce la cuota diferencial.

English often works the same way: The withholding reduces the tax balance.

In the normal word order here, Spanish follows subject + verb + object:

• La retención = subject
• reduce = verb
• la cuota diferencial = direct object

So the thing doing the action is la retención, and the thing being affected is la cuota diferencial.

Reducir is the infinitive, meaning to reduce.
Here you need a conjugated verb because the sentence says what something does.

The subject is la retención, which is third person singular, so the verb becomes:

• reducir → reduce

Examples:

• La retención reduce... = The withholding reduces...
• Las retenciones reducen... = The withholdings reduce...

Because retención is a feminine noun, so it takes la.

A very useful pattern is that nouns ending in -ción are usually feminine:

• la retención
• la información
• la declaración
• la situación

So even if the meaning is abstract, the grammatical gender is feminine.

Because diferencial and diferente do not mean exactly the same thing.

• diferente usually means different
• diferencial usually means differential, resulting, or refers to a specific technical category

In tax language, cuota diferencial is a fixed technical term. It does not simply mean different amount. It refers to a specific tax figure/result.

So this is not just a random adjective choice; it is standard tax vocabulary.

Yes. In tax and administrative Spanish, cuota diferencial is a standard term.

That matters because learners sometimes try to translate each word separately, but in technical language it is better to treat the whole phrase as one unit.

So:

• cuota = amount, quota, assessment, charge, etc. depending on context
• cuota diferencial = a specific tax amount/result after certain calculations

Because la cuota diferencial is a direct object referring to a thing, not a person.

Spanish uses the personal a mainly with specific human direct objects:

• Veo a María.
• Llamo al profesor.

But with things, you normally do not use a:

• Reduce la cuota diferencial.

So the absence of a here is exactly what you should expect.

The written accent shows that the stress falls on the last syllable:

• re-ten-ción

Without the accent mark, Spanish stress rules would make it sound wrong.

General rule:

• Words ending in n, s, or a vowel are normally stressed on the second-to-last syllable.
• If the stress is somewhere else, Spanish writes an accent mark.

Since retención ends in n but is stressed on the final syllable, it needs the accent.

Because in Spanish, adjectives often come after the noun, especially when they classify or define the noun.

So:

• cuota diferencial

This is very common in technical, legal, and formal language.

If you are an English speaker, this may feel reversed, since English usually puts adjectives before nouns:

• differential amount
• special tax amount

But Spanish normally places many descriptive or classifying adjectives after the noun.

Yes, but the given order is the most neutral and standard one.

Normal order:

• La retención reduce la cuota diferencial.

You might also see reordering for emphasis, but it would be less neutral and often need extra structure, for example:

• La cuota diferencial la reduce la retención.

That version emphasizes la cuota diferencial, but the original sentence is the clearest standard form.

Yes, it could be plural if the meaning required it.

Here the sentence uses a singular subject:

• La retención reduce...

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

• Las retenciones reducen la cuota diferencial.

So this sentence is a good example of subject-verb agreement:

• singular noun → singular verb
• plural noun → plural verb

Yes, very formal and technical. It sounds like tax, legal, or administrative Spanish rather than everyday conversation.

Words like:

• retención
• cuota diferencial

are common in official or financial contexts. So this is the kind of sentence you might read in a tax form, government website, or accounting explanation.

In everyday conversation, a speaker might explain the idea in a less technical way, depending on the exact context. For example, they might use a more explanatory sentence instead of the official term.

But in official Spanish, La retención reduce la cuota diferencial is concise and natural.

So as a learner, it is useful to recognize that:

• grammatically, the sentence is straightforward
• vocabulary-wise, it is specialized and formal