00421: VAT amount not calculated correctly
What it means
SdI code 00421 means the tax in a VAT breakdown block (2.2.2.6 Imposta) differs by at least one cent from the taxable amount (2.2.2.5) multiplied by the rate (2.2.2.1), divided by 100 and rounded to two decimals.
The usual cause
Check whether the tax was rounded differently or calculated per line and summed. SdI accepts a difference of less than one cent.
How to fix it
Recalculate Imposta as ImponibileImporto times AliquotaIVA divided by 100, rounding to two decimals: round down if the third decimal digit is less than 5, and up if it is 5 or more. Send the file again.
Elements the check reads
-
2.2.2.6 Imposta -
2.2.2.1 AliquotaIVA -
2.2.2.5 ImponibileImporto
The code as published
Read the official document . Source: Elenco dei controlli effettuati sul file fattura del Sistema di Interscambio, version 2.0, published by Agenzia delle Entrate, fatturapa.gov.it, read on 8 November 2026.
Klarbon explains each code in its own words; the official wording is in the document linked above.
Look at your file
Open the invoice in your browser to find the fields this code names: Open an Italian FatturaPA invoice. Open an Italian FatturaPA invoice
Other SdI codes
- 00400 Nature code missing on a line at zero VAT
- 00401 Nature code on a line with VAT
- 00403 Invoice date in the future
- 00411 Withholding data missing for lines with withholding
- 00413 Nature code missing on a pension fund contribution at zero VAT
- 00414 Nature code on a pension fund contribution with VAT
- 00415 Withholding data missing for a pension fund contribution
- 00417 Buyer has neither VAT number nor tax number
- 00418 Credit note dated before the invoice it corrects
- 00419 VAT breakdown missing for a rate
- 00420 Reverse charge nature with split payment
- 00422 Taxable amount not calculated correctly
- 00423 Line total not calculated correctly
- 00424 VAT rate not given as a percentage
- 00425 Invoice number has no digits
- 00427 Recipient code length does not fit the format
- 00428 Format does not match the version attribute
- 00429 Nature code missing in a VAT breakdown at zero rate
- 00430 Nature code in a VAT breakdown with a rate
- 00437 Document discount without a percentage or amount
- 00438 Line discount without a percentage or amount
- 00443 VAT rate with no matching summary
- 00444 Nature code with no matching summary
- 00445 Generic nature code no longer allowed
- 00471 Seller and buyer must differ for this document type
- 00472 Seller and buyer must be the same for this document type
- 00473 Seller's country not allowed for this document type
- 00474 Zero VAT rate not allowed for this document type
- 00475 Buyer's VAT number required for this document type
- 00476 Neither VAT country code identifies Italy
- 00477 Declaration of intent no longer valid