Абонентская плата зависит от тарифной ставки.

Because it is the subject of the sentence — the thing that depends on something.

• абонентская плата = the subscription fee / monthly fee
• зависит = depends

In Russian, the subject normally appears in the nominative case, so:

• абонентская — nominative feminine singular
• плата — nominative feminine singular

The adjective agrees with the noun in gender, number, and case.

The verb зависеть simply takes the pattern от + genitive in Russian.

So:

• зависеть от чего? = to depend on what?

This is just the normal government pattern of the verb, and it has to be memorized as part of the verb:

• зависеть от погоды = to depend on the weather
• зависеть от цены = to depend on the price
• зависеть от обстоятельств = to depend on circumstances

So in your sentence, от is there because зависеть requires it.

Because the preposition от requires the genitive case.

The basic dictionary form is:

• тарифная ставка = tariff rate / rate

After от, both words change to genitive singular:

• тарифная → тарифной
• ставка → ставки

So:

• от тарифной ставки = from / on the tariff rate

This is a very common Russian pattern: after a preposition, the noun often changes case, and any adjective with it changes too.

This is adjective–noun agreement in the genitive singular feminine.

Base form:

• тарифная ставка

Genitive singular:

• тарифной ставки

Why feminine? Because ставка is a feminine noun.

So the adjective must match it:

• nominative feminine singular: тарифная
• genitive feminine singular: тарифной

And the noun changes too:

• ставка → ставки

This kind of matching is one of the core features of Russian grammar.

It is very much a standard expression.

In real Russian, абонентская плата commonly means:

• subscription fee
• monthly service fee
• recurring fee for access to a service

So although it is literally something like subscriber fee or subscription-related payment, learners should treat it as a set phrase.

You will often see it in contexts like:

• mobile plans
• internet service
• utilities
• cable TV
• software/services

It comes from абонент = subscriber / customer using a service line or account.

The adjective абонентский / абонентская / абонентское means something like:

• subscriber-related
• subscription-related

In the phrase абонентская плата, it does not usually mean a random payment made by a subscriber. It means the regular fee charged for having the service.

So this is more idiomatic than purely literal.

Зависит is:

• present tense
• 3rd person singular
• from the verb зависеть = to depend

So the full logic is:

• абонентская плата = singular subject
• therefore the verb is singular: зависит

This present tense is often used in Russian for general facts or rules, just like in English:

• Цена зависит от спроса.
• Результат зависит от условий.

So in your sentence, it describes a general relationship, not just something happening right now.

Yes. Russian word order is more flexible than English because the cases show the grammatical roles.

The neutral order here is:

• Абонентская плата зависит от тарифной ставки.

But other orders are possible for emphasis, for example:

• От тарифной ставки зависит абонентская плата.

That version puts more focus on от тарифной ставки.

Even so, the original order is the most natural and neutral in a standard statement.

Yes, that can also be correct, but the meaning is slightly less specific.

• от тарифа = on the tariff / on the plan
• от тарифной ставки = on the tariff rate

The version with тарифа sounds more general and is common in everyday speech. The version with тарифной ставки sounds a bit more formal, technical, or contractual.

So both can work, but they are not always identical in tone or precision.

The stress is:

• абоне́нтская
• пла́та
• зави́сит
• тари́фной
• ста́вки

A rough English-friendly pronunciation would be:

a-ba-NYENT-ska-ya PLA-ta za-VEE-sit ot ta-REEF-noy STAV-kee

Pay special attention to the unstressed vowels, because in real Russian they are reduced in pronunciation.

Because the sentence is talking about the fee and the tariff rate as general concepts.

Russian often uses the singular this way, just like English does:

• Price depends on quality.
• Success depends on preparation.

So:

• абонентская плата = the subscription fee, as a category or standard fee
• тарифная ставка = the tariff rate, as a category or determining factor

If you were talking about multiple fees or multiple rates, then you would use plural forms instead.