La base liquidable afecta a la cuota diferencial.

Because the verb afectar is commonly used with the preposition a in Spanish: afectar a algo / afectar a alguien.

So:

• afecta a la cuota diferencial = affects the final tax amount / differential quota

This a is part of the verb pattern here, not the so-called personal a.

More examples:

• Esto afecta a todos.
• La medida afecta a las empresas pequeñas.

In some contexts you may see afectar without a, but with this meaning, afectar a is the normal and safest pattern to learn.

Spanish usually uses definite articles more often than English does.

So even if English might say something like:

• Taxable base affects final tax liability

Spanish normally says:

• La base liquidable afecta a la cuota diferencial.

Both noun phrases take the article because they are being treated as specific concepts within the tax system:

• la base liquidable
• la cuota diferencial

This is very natural in formal or technical Spanish.

Because the subject is la base liquidable, which is singular.

Breakdown:

• La base liquidable = subject
• afecta = verb
• a la cuota diferencial = object/complement

Since base is singular, the verb must also be singular:

• la base ... afecta

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

• Las bases liquidables afectan a la cuota diferencial.

Because the main noun is base, and base is a feminine noun in Spanish:

• la base

The adjective liquidable has the same form for masculine and feminine singular, because adjectives ending in -e or many ending in -able / -ible often do not change for gender:

• base liquidable
• importe liquidable

It does change for number:

• singular: liquidable
• plural: liquidables

So:

• la base liquidable
• las bases liquidables

Diferencial is an adjective describing cuota.

In Spanish, adjectives often come after the noun, especially in technical or neutral language. So:

• cuota diferencial = differential/final resulting quota (depending on the tax context)

This word order is completely normal:

• noun + adjective

Other examples:

• tipo impositivo
• base imponible
• deuda tributaria

In tax language, these combinations are often fixed terms, so it is best to learn them as whole expressions.

Yes. Afecta is the third-person singular present indicative of afectar.

Here it is not talking about something happening right now in a dramatic sense. It is using the present to state a general fact or rule:

• La base liquidable afecta a la cuota diferencial.

This is very common in explanations, textbooks, legal language, and technical writing.

It works like English sentences such as:

• Water boils at 100°C.
• Interest rates affect borrowing costs.

A native speaker might understand it, but in standard usage afectar a is the more natural and expected form here.

So for learners, the recommended version is:

• La base liquidable afecta a la cuota diferencial.

Especially in careful, formal, or technical Spanish, keeping the a is a good idea.

Yes, but the original order is the most neutral and natural:

• La base liquidable afecta a la cuota diferencial.

You could change the order for emphasis, but it would sound more marked or formal:

• A la cuota diferencial la afecta la base liquidable.

That version is grammatically possible, but much less natural as a basic explanatory sentence.

For learners, the best default is:

• subject + verb + a + object

Not really. It is correct Spanish, but it belongs to tax/legal/administrative language, especially in Spain.

Words like these are technical terms:

• base liquidable
• cuota diferencial

So a native speaker would understand that this sentence comes from a tax explanation, official document, or accounting context, not from casual conversation.

A simple breakdown is:

• La base liquidable = the subject
• afecta = the verb
• a la cuota diferencial = the complement/object affected

More specifically:

• la = definite article
• base = noun
• liquidable = adjective
• afecta = present tense verb
• a = preposition required by afectar a
• la = definite article
• cuota = noun
• diferencial = adjective

Seeing the structure clearly can make technical Spanish much easier to read.

Yes, that is a very good idea.

In technical Spanish, many noun + adjective combinations work almost like fixed labels. If you learn them as separate words only, you may understand less quickly. If you learn them as chunks, reading becomes easier.

For example, it helps to store these as whole terms:

• base imponible
• base liquidable
• cuota íntegra
• cuota líquida
• cuota diferencial

That is especially useful in Spanish tax vocabulary, where small wording changes can refer to different official concepts.