Overview
P_11 is the net value of a single line item (in Polish, "wartość netto pozycji"). It sits inside each FaWiersz block and is the value of that line before any VAT is added.
P_11 is required on every line and is an amount field (TKwotowy in the XSD). It is written as a decimal number with up to two decimal places and a dot as the separator. A value such as 1000.00 is valid; 1000,00 is not.
The net value is calculated from two other fields on the same line: the unit net price (P_9A) and the quantity (P_8B). You multiply them and round the result to two decimals. If a line has a unit net price of 150.50 and a quantity of 2, the net value is 301.00.
VAT is not computed per line: lines with the same P_12 rate are summed into P_13_x, and the VAT (P_14_x) is computed once on that sum, rounded to two decimals. Because P_11 is net, it must not include VAT. A common integration mistake is to copy the gross value of a line into P_11 and then also add VAT on top, which double-counts the tax and makes the invoice total wrong. Keep P_11 strictly net, and let the VAT summary fields handle the tax.
There are three practical checks worth running before you submit. First, verify that P_11 equals P_9A times P_8B for every line (when the unit price has at most two decimals). Second, confirm that the sum of all P_11 values matches the net total per rate in the Fa summary (P_13_x). Third, remember that rounding happens at the line level (P_11) and once more per VAT rate when the VAT amount (P_14_x) is computed. These checks catch most discrepancies before the document reaches KSeF.
In Notaly you do not write P_11 yourself; the API calculates it from the unitNetPrice and quantity properties you send, writes it to the line and keeps it consistent with the totals. That removes the most common source of arithmetic mistakes on the invoice.
A complete, valid FA(3) example appears below, with P_11 filled on both lines.
<Faktura xmlns="http://crd.gov.pl/wzor/2025/06/25/13775/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<Naglowek>
<KodFormularza kodSystemowy="FA (3)" wersjaSchemy="1-0E">FA</KodFormularza>
<WariantFormularza>3</WariantFormularza>
<DataWytworzeniaFa>2026-10-12T07:23:07Z</DataWytworzeniaFa>
<SystemInfo>einvoice-api</SystemInfo>
</Naglowek>
<Podmiot1>
<DaneIdentyfikacyjne><NIP>2745013933</NIP><Nazwa>Example Sp. z o.o. (FICTIONAL)</Nazwa></DaneIdentyfikacyjne>
<Adres><KodKraju>PL</KodKraju><AdresL1>ul. Testowa 1, 00-001 Warszawa</AdresL1></Adres>
</Podmiot1>
<Podmiot2>
<DaneIdentyfikacyjne><NIP>1234563218</NIP><Nazwa>Test Customer S.A. (FICTIONAL)</Nazwa></DaneIdentyfikacyjne>
<Adres><KodKraju>PL</KodKraju><AdresL1>ul. Probna 2, 30-001 Kraków</AdresL1></Adres>
<JST>2</JST>
<GV>2</GV>
</Podmiot2>
<Fa>
<KodWaluty>PLN</KodWaluty>
<P_1>2026-10-12</P_1>
<P_2>FV/2026/10/001</P_2>
<P_13_1>1000.00</P_13_1><P_14_1>230.00</P_14_1>
<P_13_2>301.00</P_13_2><P_14_2>24.08</P_14_2>
<P_15>1555.08</P_15>
<Adnotacje>
<P_16>2</P_16><P_17>2</P_17><P_18>2</P_18><P_18A>2</P_18A>
<Zwolnienie><P_19N>1</P_19N></Zwolnienie>
<NoweSrodkiTransportu><P_22N>1</P_22N></NoweSrodkiTransportu>
<P_23>2</P_23>
<PMarzy><P_PMarzyN>1</P_PMarzyN></PMarzy>
</Adnotacje>
<RodzajFaktury>VAT</RodzajFaktury>
<FaWiersz>
<NrWierszaFa>1</NrWierszaFa>
<P_7>SaaS subscription - October</P_7>
<P_8A>pcs.</P_8A>
<P_8B>1</P_8B>
<P_9A>1000.00</P_9A>
<P_11>1000.00</P_11>
<P_12>23</P_12>
</FaWiersz>
<FaWiersz>
<NrWierszaFa>2</NrWierszaFa>
<P_7>Support</P_7>
<P_8A>hrs.</P_8A>
<P_8B>2</P_8B>
<P_9A>150.50</P_9A>
<P_11>301.00</P_11>
<P_12>8</P_12>
</FaWiersz>
</Fa>
</Faktura>Sources
Source: crd.gov.pl