Należność jest wyższa, odkąd wzrosła stawka tej taryfy.

Here należność means something like the amount due, the payable amount, or the charge.

It is a fairly formal word. In everyday speech, people might more often say:

• opłata = fee / charge
• rachunek = bill
• kwota do zapłaty = amount to pay

So this sentence sounds a bit official, administrative, or billing-related.

Because wyższa agrees with należność, which is:

• feminine
• singular

The adjective has to match the noun, so:

• masculine: wyższy
• feminine: wyższa
• neuter: wyższe

Also, wyższa is the comparative form of wysoka / wysoki, so it means higher.

Polish, like English, often uses higher/lower for amounts, prices, fees, and charges.

In a normal Polish sentence, you need the verb być in the present tense here:

• Należność jest wyższa. = The amount due is higher.

Unlike in Russian, for example, Polish normally does not drop the present-tense is in standard sentences like this.

You may sometimes see the verb omitted in headlines, notes, or very elliptical style, but in ordinary grammar jest is needed.

Because after być with an adjective, Polish uses the nominative form of the adjective.

So:

• Należność jest wyższa. — correct

not:

• Należność jest wyższą.

The form wyższą would be accusative or instrumental feminine singular, and it does not fit here.

Odkąd means since or from the time when.

It introduces a point in time that started in the past and is still relevant now. So the structure is roughly:

• X is now true, odkąd Y happened
• X has been true since Y happened

In this sentence, it has a strong time meaning, but in English the natural translation may also sound slightly causal, because the increase in the rate explains why the amount due is higher.

• bo = because
• ponieważ = because / since
• odkąd = since, in the sense of from the time when

So:

• Należność jest wyższa, bo wzrosła stawka tej taryfy.
  = The amount due is higher because the rate increased.

• Należność jest wyższa, odkąd wzrosła stawka tej taryfy.
  = The amount due has been higher since the rate increased.

With odkąd, the idea is not just cause, but also the time period starting from that change.

Wzrosła is the past tense of the perfective verb wzrosnąć, meaning to rise / to increase.

It is used because the sentence refers to a completed change in the past:

• first, the rate went up
• as a result, the amount due is now higher

If you used an imperfective form like rosła, it would suggest an ongoing or repeated process:

• rosła = was increasing / used to increase

That is not the idea here. Here the speaker means a completed increase, so wzrosła is the natural choice.

Because the subject of that clause is stawka, and stawka is feminine singular.

In the Polish past tense, the verb agrees in gender and number:

• masculine: wzrósł
• feminine: wzrosła
• neuter: wzrosło
• plural: wzrosły

So:

• stawka wzrosła = the rate increased

Tej taryfy is in the genitive case.

The phrase means:

• stawka = rate
• tej taryfy = of this tariff / of this tariff plan

So the whole phrase is:

• stawka tej taryfy = the rate of this tariff

Form by form:

• dictionary form: ta taryfa
• genitive singular: tej taryfy

This kind of noun + genitive structure is very common in Polish.

Sometimes yes, but in Polish taryfa is often used more broadly for a pricing plan, rate schedule, or set of charges.

Depending on context, it could refer to things like:

• electricity or gas pricing
• phone plans
• transport fares
• service charges

So stawka tej taryfy may sound more natural in Polish than the literal English-looking phrase the rate of this tariff.

Yes. Polish word order is flexible.

For example, you could also say:

• Odkąd wzrosła stawka tej taryfy, należność jest wyższa.

This puts the since-clause first, which may feel slightly more natural in English-style structuring.

The original sentence puts the result first:

• Należność jest wyższa, odkąd...

That can give a little more emphasis to the present situation.

Yes, it sounds fairly formal or administrative.

A more everyday version might be:

• Opłata jest wyższa, odkąd wzrosła stawka tej taryfy.
• Opłata jest teraz wyższa, bo wzrosła stawka.

The original version is perfectly correct, but należność gives it a more official tone, as if from a bill, notice, or customer-service message.