Which NBP rate do I use on a foreign-currency invoice?

The average NBP rate from the last business day before the tax obligation arises (art. 31a(1)). If you issue the invoice before the tax obligation arises, you use the rate from the last business day before the invoice date (art. 31a(2)). You convert the VAT amount into złoty at that rate.

Do I convert the whole invoice into złoty?

No. You always report the VAT amount in złoty, but the net and gross amounts can stay in the foreign currency. The złoty figure at the correct rate applies to the VAT alone.

What if the preceding day is a weekend or public holiday?

You take the rate from the last business day before — skipping weekends and holidays. That's why pulling the correct NBP table automatically removes the guesswork.

NBP Exchange Rates on Invoices: Converting Foreign Currency in KSeF

Q: Can I use the ECB rate instead of the NBP rate?

Yes. Instead of the average NBP rate you may use the average European Central Bank (ECB) rate from the last day before. That is a permitted alternative; a commercial bank's rate is not.

You always report the VAT amount in złoty at the average NBP rate from the last business day before the tax obligation arises (art. 31a(1)). If the invoice is issued earlier, use the rate from the day before it was issued (art. 31a(2)). Net and gross amounts can stay in the foreign currency.

Which NBP rate goes on a foreign-currency invoice?

You use the average NBP rate from the last business day before the day the tax obligation arises (art. 31a(1) of the VAT Act). What matters is the tax obligation, not the date on the document.

Exception: an invoice issued before the tax obligation

If you issue the invoice before the tax obligation arises, you read the rate differently. In that case you take the average NBP rate from the last business day before the invoice date (art. 31a(2)). The two cases in brief:

Invoice on time or after the tax obligation → rate from the business day before the day the tax obligation arises.
Invoice before the tax obligation → rate from the business day before the invoice date.

Instead of the NBP rate, you may also use the average European Central Bank (ECB) rate from the last day before.

Example

The tax obligation arises on 10 June (Wednesday). You convert the VAT amount at the average NBP rate from 9 June (Tuesday) — the last business day before. If 9 June fell on a Sunday, you go back to the last business day, for example Friday.

Most common mistakes

Using the rate from the issue date instead of the day before — the most frequent slip.
Confusing the tax obligation with the invoice date — for an invoice issued before the tax obligation, the issue date is what counts.
Skipping a weekend or holiday — you have to go back to a business day.
Using a rate other than the average NBP (or ECB) — for example a commercial bank's rate; that's an error.

Automatic NBP rates

Checking NBP tables by hand for every invoice is tedious and error-prone. KSeF Kit pulls the correct average NBP rate automatically for each invoice's date and shows it clearly — so you have full transparency into the rate at which the invoice was filed. See the export invoice and how to issue an invoice.