TAX_CALCULATION_MISMATCH: Tax calculation error

StandardKSeF FA(3), Polish national e-invoicing systemSeverityError: the invoice is rejectedSyntaxFA(3) XMLApplies toStructured invoices (FA(3) schema) submitted to the Polish KSeF. XSD codes come from the schema, semantic codes from the Ministry of Finance information sheet; KSeF rejects invoices that fail an error-level rule.

Official rule text

[TAX_CALCULATION_MISMATCH] Tax calculation error: P_14_x must equal P_13_x × (P_12 rate / 100), and P_15 must equal sum of all (P_13_x + P_14_x)

Why this error occurs

KSeF checks the FA(3) XML in two stages: XSD schema (structure, element order, data types, patterns such as NIP or dates) and semantic rules from the Ministry of Finance information sheet (consistency of amounts, annotations P_16 to P_23, roles of Podmiot2/Podmiot3, bank account formats, currency rates).

How to fix it

Fix the element named in the message. For XSD errors compare the element order and value pattern with the FA(3) schema; for semantic errors apply the cause and fix hints listed on this page. Re-validate before submitting to KSeF: a rejected invoice has no KSeF number and is not issued.

What the validator checks

Check levelsemantic / business_logic

Typical causes

Incorrect tax amount calculation
Rounding errors in tax calculations
Total amount does not match sum of base amounts and taxes

Check your invoice

Drop your XML or PDF on the validator and every failed rule is linked to its page here. Free, no account, the file is not stored.

Check your invoice →

Same check via API:

curl -F file=@invoice.xml https://einvoicechecker.com/v1/validate

Related rules

CURRENCY_RATE_MISMATCH KursWaluty does not match the NBP Table A mid-rate for the reference date (Art
CURRENCY_RATE_UNVERIFIABLE KursWaluty cannot be verified — NBP rate unavailable or outside the valid date window (Art
FOREIGN_CURRENCY_TAX_PLN Foreign currency invoice with tax amounts should include PLN conversions in P_14_*W…
KURS_WALUTY_Z_PLACEMENT KursWalutyZ at Fa level is ONLY valid for advance invoices (RodzajFaktury = ZAL or…
NEGATIVE_QUANTITY_NOT_ALLOWED Negative quantities (P_8B) are only allowed in corrective invoices (RodzajFaktury =…
NIP_IN_WRONG_FIELD Polish NIP detected in NrVatUE field - must be in NIP field for purchaser KSeF access…
OO_RATE_FOREIGN_BUYER P_12 = 'oo' is for domestic reverse charge only
P12_ENUMERATION P_12 must be one of

Frequently asked questions

What does TAX_CALCULATION_MISMATCH mean?

TAX_CALCULATION_MISMATCH is a ksef fa(3) rule: Tax calculation error: P_14_x must equal P_13_x × (P_12 rate / 100), and P_15 must equal sum of all (P_13_x + P_14_x)

Will my invoice be rejected because of TAX_CALCULATION_MISMATCH?

Yes. TAX_CALCULATION_MISMATCH is flagged "fatal"; validators (KoSIT, Peppol access points, the German ZRE/OZG-RE portals, KSeF) reject the invoice until it is fixed.

Which formats does TAX_CALCULATION_MISMATCH apply to?

Structured invoices (FA(3) schema) submitted to the Polish KSeF. XSD codes come from the schema, semantic codes from the Ministry of Finance information sheet; KSeF rejects invoices that fail an error-level rule. Syntax: FA3.

Source: KSeF FA(3) schema 1-0E + semantic rules (@ksefuj/validator 0.4). Catalogue generated from the official rule sets on 2026-10-15.