Amounts on foreign-currency invoices are converted into złoty at the mid-market NBP rate published on the last working day preceding the date of revenue or cost. When payment arrives later and at a different rate, an exchange-rate difference arises: a positive one increases revenue, a negative one — costs. These rules apply to entrepreneurs taxed on the tax scale or on the flat tax (podatek liniowy); below we show them with numbers and explain the separate rules for VAT.
Three dates that decide the rate
A single foreign-currency transaction features several dates, each with its own meaning:
- revenue date — as a rule, the day the service is performed or the goods are released, and no later than the day the invoice is issued or payment is received,
- cost date — for taxpayers keeping the tax book of revenue and expenditure (KPiR) on an accrual basis, this is the day the invoice is issued; in full accounting books — the day the cost is recognised on the basis of the invoice,
- payment date — the day money comes in or goes out; this is what closes the transaction and sets the FX difference.
For converting revenue and cost, you take the mid-market NBP rate from the last working day before the date in question. If the service is performed on a Monday, the Friday rate applies.
How an FX difference arises — the mechanics
The PIT Act compares two złoty values of the same foreign-currency amount: the one converted at the rate for the revenue (or cost) date and the one at the payment date.
| Situation | Rate on the payment date vs. the revenue/cost date | Effect |
|---|---|---|
| Sale (receivable from the customer) | higher | positive difference — increases revenue |
| Sale (receivable from the customer) | lower | negative difference — increases costs |
| Purchase (payable to the supplier) | higher | negative difference — increases costs |
| Purchase (payable to the supplier) | lower | positive difference — increases revenue |
On the payment date, the rate actually applied is used — for example a bank's exchange counter rate on conversion. If the money lands on a foreign-currency account and is not converted, there is no actual rate to use — in that case the payment-date rate is also the mid-market NBP rate published on the last working day before that date.
Example: a euro invoice for a German customer
A developer running a business taxed under the flat tax performs a service on 30 September 2026 and issues an invoice for EUR 8,000 the same day. The rates in the example are illustrative.
- Revenue: the mid-market NBP rate on 29 September is PLN 4.25. Revenue is 8,000 × 4.25 = PLN 34,000.
- Payment: the customer pays on 14 October into the euro account. The NBP rate on 13 October is PLN 4.31, so the payment is worth PLN 34,480.
- Difference: 34,480 − 34,000 = PLN 480 of positive FX difference, which increases October's revenue.
- Conversion: if in November the entrepreneur converts the funds into złoty at the bank at a rate of PLN 4.28, another difference arises — this time negative — on own funds (PLN 34,240 against PLN 34,480, i.e. a cost of PLN 240).
For an invoice to a Polish counterparty with VAT in a foreign currency, FX differences are calculated only on the net amount. Differences attributable to VAT do not affect income tax.
Rate for VAT — different rules from PIT
The VAT Act provides its own moment for conversion:
- by default — the mid-market NBP rate from the last working day before the tax obligation arises,
- if the invoice is issued before the tax obligation arises — the rate from the last working day before the invoice date,
- alternatively — the last European Central Bank rate from the day before the tax obligation arose,
- optionally — the conversion rules used by the taxpayer in income tax; this choice is binding for at least 12 consecutive months.
The last option lets you align the rate in PIT and VAT, which cuts the number of conversions in your records. For services to foreign businesses where VAT is settled by the buyer, the rate matters mostly for reporting the sale in the JPK file. We cover the basics of VAT in our article on VAT in Poland.
The most common mistakes
- Taking the rate from the invoice date instead of the day before — a small change in the rate, but an error that runs through the whole set of records.
- Skipping differences when funds come to a foreign-currency account — the lack of conversion does not exempt you from measuring them.
- Counting differences on VAT — the VAT part is left out of PIT.
- Omitting differences in the IP Box register — under the 5% relief, differences on revenue from qualified rights affect the income covered by the preference; more in our article on IP Box.
- A rate significantly off the market — if the rate actually applied differs from the NBP rate by more than 5%, the tax office may ask for an explanation or a change in the value.
Entrepreneurs under ryczałt (lump-sum tax on recorded revenue) also convert revenue at the NBP rate from the preceding day, and apply the same rules to FX differences, except that negative differences are not a cost; they reduce revenue in the year in which they arose.
How Good Balance can help
We keep records with automatic conversion at NBP rates and settle FX differences — within our full accounting for companies and in support for entrepreneurs. We also help you correctly issue VAT invoices in a foreign currency with the tax amount converted to złoty.