🧾 Introduction
If you buy the same stock or ETF in multiple transactions at different prices, you must calculate the average purchase cost when you later sell.
This rule ensures that the taxable profit in your PIT-38 is accurate and based on actual investment costs.
💡 Why Average Price Matters
When you sell part or all of your holdings, you cannot choose which units were sold. Polish tax law follows the FIFO (First In, First Out) principle — meaning the first assets you bought are the first you sold.
To simplify, you can calculate the average cost per unit, which combines all your purchase prices and commissions into one value.
🧮 Example: Multiple ETF Purchases
| Date | Units | Price per Unit (EUR) | Total (EUR) |
|---|---|---|---|
| 1 Jan 2024 | 10 | €100 | €1,000 |
| 1 Mar 2024 | 5 | €120 | €600 |
| 1 May 2024 | 5 | €110 | €550 |
Total units = 20
Total cost = €1,000 + €600 + €550 = €2,150
Average price = 2,150 / 20 = €107.50 per unit
If you sell 10 units later at €115 each:
Profit per unit = 115 − 107.5 = €7.5
Total profit = €75 (before conversion to PLN).
💱 Convert to PLN Using NBP Rates
Each purchase and sale must be converted to PLN using the NBP average rate from the day before the transaction.
If you bought in EUR and sold in EUR, use the correct rates for each date. Example:
| Date | Event | Rate | Amount (EUR) | PLN |
|---|---|---|---|---|
| 1 Jan 2024 | Purchase | 4.40 | €1,000 | 4,400 |
| 1 Mar 2024 | Purchase | 4.45 | €600 | 2,670 |
| 1 May 2024 | Purchase | 4.50 | €550 | 2,475 |
| 1 Sep 2024 | Sale | 4.60 | €1,150 | 5,290 |
📄 How to Declare in PIT-38
| Field | Description | PLN |
|---|---|---|
| 22 | Income (from sale) | 5,290 |
| 23 | Costs (total from purchases) | 9,545 |
| 26 | Loss or Profit | depends on totals |
Attach the correct PLN conversions and keep your trade statements as evidence.
⚠️ Tips for Investors
- Keep a spreadsheet of all purchases with NBP rates.
- Remember FIFO order if you sell only part of your holdings.
- Include all commissions in your average cost.
- Never use a single "average" exchange rate for all transactions.
By calculating average purchase cost correctly, you can avoid errors in your PIT-38 and ensure you pay only the necessary tax.