Налогообложение проверяют исходя из налоговой базы.

Because налогообложение is not the subject here. It is the object: the thing being checked.

The verb проверяют is in the 3rd person plural and has an unstated subject, something like they check. In Russian, this is very common when the speaker means:

• people check
• officials check
• the authorities check
• someone checks, without naming exactly who

So the structure is basically:

• [They] check taxation based on the tax base.

Russian often uses this indefinite-personal construction where English might use they, people, or a passive.

There are two main clues:

1. The verb form

   • проверяют = they check
   • If налогообложение were the subject, the verb would need to agree with it:
     • Налогообложение проверяет would mean Taxation checks..., which does not make sense here.

2. Case form

   • Налогообложение is a neuter inanimate noun.
   • In Russian, for inanimate neuter nouns, the nominative and accusative look the same.
   • So the form налогообложение could theoretically be either subject or object, but the verb and meaning show that here it is the accusative object.

So this is one of those sentences where form alone is not enough; you use grammar plus context.

Исходя из means something like:

• based on
• proceeding from
• using as a basis
• on the basis of

In this sentence, it tells you what basis is used for the checking.

So:

• исходя из налоговой базы = based on the tax base

A useful thing to know is that исходя из originally comes from the verb исходить из. In modern usage, though, learners often treat it as a fixed expression meaning based on.

It is common in formal, legal, administrative, and academic Russian.

Because из requires the genitive case, and исходя из keeps that same pattern.

The base form is:

• налоговая база = tax base

But after из, it becomes genitive:

• из налоговой базы

That means:

• налоговая → налоговой
• база → базы

So the phrase is in the genitive singular.

Yes, it is very common.

This is called an indefinite-personal construction. Russian uses the 3rd person plural without naming the subject when the doer is:

• unknown
• unimportant
• obvious from context
• meant in a general institutional sense

Examples:

• Говорят, что... = They say that... / It is said that...
• Меня спросили. = They asked me.
• Здесь не курят. = People do not smoke here.

So in your sentence, проверяют suggests something like:

• the tax authorities check
• inspectors check
• they check

without explicitly stating who they are.

Because the sentence describes a general procedure, regular practice, or how something is done, not a single completed action.

• проверяют = imperfective
  • they check / they are checking / they check as a rule
• проверят = perfective
  • they will check / they will complete the check once

In formal statements about rules, methods, and repeated actions, Russian usually prefers the imperfective.

So here the idea is not they will check it one time, but rather this is the basis on which taxation is checked.

Yes. A passive-style version would be:

• Налогообложение проверяется исходя из налоговой базы.

That means roughly the same thing: Taxation is checked based on the tax base.

The difference is mostly stylistic:

• проверяют = active form with an unspecified they
• проверяется = passive-style presentation focusing on the process itself

Russian often prefers the active plural with an omitted subject, especially in official or procedural language, where English might choose a passive more often.

Yes, but not in a dramatic way.

Russian word order is more flexible than English. Here, starting with Налогообложение puts the focus first on what is being checked.

So the sentence structure is roughly:

• Налогообложение — topic / what we are talking about
• проверяют — what people do to it
• исходя из налоговой базы — the basis they use

This order sounds natural in formal writing.

A version with an explicit subject could be:

• Налоговые органы проверяют налогообложение исходя из налоговой базы.

But in the original sentence, leaving out the subject keeps it more impersonal and bureaucratic in tone.

For most learners, it is best to learn it as a fixed phrase meaning based on.

Historically, исходя is a verbal adverb form from исходить, so grammatically it has a verbal origin. But in many modern formal sentences, исходя из functions almost like a set prepositional expression.

So for practical purposes, learn:

• исходя из + genitive = based on / proceeding from

That will help you recognize and use it correctly much faster than trying to build it from the verb each time.

Here is the breakdown:

• Налогообложение

  • neuter singular
  • here it is the direct object in the accusative
  • same form as nominative because it is inanimate

• проверяют

  • verb, 3rd person plural
  • imperfective
  • present tense
  • means they check

• исходя из

  • fixed expression meaning based on
  • followed by the genitive

• налоговой базы

  • genitive singular
  • from налоговая база

So structurally, the sentence is:

• Object + verb + basis phrase

which is a very normal Russian pattern in this kind of formal style.