Nadpłata jest duża.

Nadpłata is a feminine noun.

A very common clue in Polish is the ending -a: many nouns ending in -a are feminine. In this sentence, you can also see the gender from the adjective: duża is the feminine form of big/large.

So:

• nadpłata = feminine
• duża = feminine singular form

Because Polish adjectives must agree with the noun in gender, number, and case.

Here, nadpłata is:

• feminine
• singular
• nominative

So the adjective must also be feminine singular nominative:

• masculine: duży
• feminine: duża
• neuter: duże

That is why the sentence has duża.

It is in the nominative case.

Why? Because nadpłata is the subject of the sentence: it is the thing being described as large.

In Nadpłata jest duża, the structure is basically:

• nadpłata = subject
• jest = is
• duża = predicate adjective

The adjective duża is also in the nominative form, agreeing with the subject.

Because after jest with an adjective, Polish uses the nominative adjective form, not dużą.

So:

• duża = nominative feminine singular
• dużą = accusative or instrumental feminine singular

In this sentence, the standard form is:

• Nadpłata jest duża.

A learner may expect a different case after to be, but with adjectives like this, Polish uses the nominative.

In normal standard Polish, yes, you need it.

Polish usually keeps the present-tense form of być (to be) in sentences like this:

• Nadpłata jest duża.

Leaving it out:

• Nadpłata duża

would sound incomplete, very colloquial, note-like, or unnatural in ordinary speech.

So for normal speaking and writing, keep jest.

The neutral, standard order is:

• Nadpłata jest duża.

Polish word order is more flexible than English, but changing the order usually changes the emphasis.

For example:

• Nadpłata jest duża. = neutral statement
• Duża jest nadpłata. = marked/emphatic, focusing on large
• Jest duża nadpłata. = possible in some contexts, but it can sound less neutral and may shift the focus

So yes, other orders are possible, but the given one is the most natural basic version.

They are related, but they are not the same structure.

• duża nadpłata = a large overpayment / the large overpayment
  This is a noun phrase. The adjective directly modifies the noun.

• nadpłata jest duża = the overpayment is large
  This is a full sentence. The adjective comes after jest and describes the subject.

So:

• duża nadpłata = phrase
• nadpłata jest duża = sentence

Because Polish does not have articles like English a/an/the.

So nadpłata can mean:

• an overpayment
• the overpayment

The exact meaning depends on context.

That is very normal in Polish. Learners often want to add an article, but Polish simply does not use one.

A rough English-friendly pronunciation is:

• naht-PWA-ta yest DOO-zha

A few important points:

• ł sounds like English w
• j sounds like English y
• ż sounds like the sound in measure or genre
• Polish stress is usually on the second-to-last syllable

So:

• nadpłata → stress on pła
• duża → stress on du

Also, in natural pronunciation, the d in nadpłata may sound closer to t because it comes before p.

It usually refers to an amount paid in excess — money that was paid above what was actually owed.

You may see it in contexts like:

• bills
• taxes
• invoices
• bank/account statements
• utility payments

So it often means something like:

• an overpayment
• excess payment
• credit balance in your favor

The exact English translation depends on context, but the basic idea is too much money has been paid.

Very simply:

• Nadpłata nie jest duża. = The overpayment is not large.
• Nadpłata była duża. = The overpayment was large.
• Nadpłata będzie duża. = The overpayment will be large.

So you can keep the same pattern:

• [noun] + jest/była/będzie + adjective

This makes the sentence a useful model for many similar Polish sentences.