How the BubbleTax tax report for Interactive Brokers works
XML in. Anlage KAP out. The calculation takes a few minutes.
BubbleTax processes your IBKR Flex-Query export under German tax law. FIFO, ECB rates, loss offsetting, every figure traceable back to the original transaction.
Also for IBKR-based brokers:Tax report for CapTraderTax report for LYNX
Three steps to your tax report
No broker connection, no credentials for your brokerage account, no data aggregation. You control what gets uploaded.
Watch the video tutorialExport.Flex Query as XML
Step-by-step guide in our knowledge base. Works for CapTrader, LYNX and Estably too.
Upload.Hand over the file
Drag-and-drop into the browser. Processing starts automatically. The preview is free and needs no credit card, but it does need an account with e-mail login.
Download.Two PDF reports
Tax summary with the values for your Anlage KAP, plus a detail report with every single transaction.
What BubbleTax Calculates
Four areas, fully under German tax law. Items with an arrow link to the in-depth explainer.
Securities
- Stocks (buy/sell with FIFO)
- ETFs with partial exemption and Vorabpauschale
- Bonds and certificates
- Options (writing, buying, closing)
- Futures and CFDs
Income
- Dividends (domestic and foreign)
- Interest and accruals
- Withholding tax credits
Currencies
- Automatic ECB rate conversion
- Foreign currency gains and losses (FIFO)
- Multi-currency support
Special Cases
- Corporate actions (splits, spin-offs, mergers)
- Correct loss offset categories
- Direct mapping to Anlage KAP lines
Other tools deliver numbers. BubbleTax delivers evidence.
You get two PDFs you can hand directly to the tax office. Every total in the summary can be traced through the detail report back to the individual IBKR transaction.
- Tax summary: All values for Anlage KAP at a glance
- Direct mapping to Anlage KAP lines
- Detail report: Every transaction individually broken down with FIFO matching
- Traceable FIFO positions – which buy was matched with which sell
- Every number traceable back to the original transaction
Which value goes into which line
The report assigns every result value to the line of the official form where it belongs. The table shows the most common values for the forms of assessment period 2025; where the 2019 to 2024 forms differ, the earlier line is shown next to it. The report always uses the lines of the respective tax year.
| Result value in the report | Form | Line (2025 form) | Line (2019 to 2024 forms) |
|---|---|---|---|
| Gains from stock sales (included in line 19) | KAP | 20 | same as 2025 |
| Losses from stock sales | KAP | 23 | same as 2025 |
| Foreign dividends | KAP | 19 | same as 2025 |
| Interest | KAP | 19 | same as 2025 |
| Options, futures and CFDs: result | KAP | 19 | 21 (und 19) |
| Options, futures and CFDs: losses | KAP | 22 | 24 |
| Option writer premiums (losses from closing trades in line 22) | KAP | 19 | 21 (und 19) |
| Foreign currency gains from interest-bearing accounts (losses in line 22) | KAP | 19 | same as 2025 |
| Creditable foreign withholding tax | KAP | 41 | same as 2025 |
| Distributions from funds and ETFs, per fund type | KAP-INV | 4 bis 8 | same as 2025 |
| Advance lump sums (Vorabpauschale), per fund type | KAP-INV | 9 bis 13 | same as 2025 |
| Gains and losses from fund sales, per fund type | KAP-INV | 14, 17, 20, 23, 26 | same as 2025 |
| Private sales of other assets, e.g. Xetra-Gold (section 23 EStG) | SO | 57 | 53 |
Because IBKR is a foreign broker, the official instructions for Anlage KAP place the income in the line for foreign capital income (line 19), not in line 18. The fund lines of Anlage KAP-INV apply per fund type (equity fund, mixed fund, real estate fund, foreign real estate fund, other fund), each before partial exemption.
Source: line mapping of the BubbleTax report, chapter reconciling the results to the tax forms. The official instructions for Anlage KAP, KAP-INV and SO remain authoritative.
What BubbleTax does not do
So that you know where you stand beforehand.
- No transmission to the tax office. There is no ELSTER interface; you transfer the values yourself or hand the report to your tax firm.
- No tax advice. BubbleTax calculates and documents. Using it does not replace tax advice and is not assistance in tax matters within the meaning of the German Tax Advisory Act.
- The review stays with you. The report discloses every calculation step so that you can check it; responsibility for the correctness of the data provided and of the return rests with you.
- Only the Flex Query export as XML. CSV files, PDF statements or data from brokers outside the IBKR platform are not read; BubbleTax has no access to your brokerage account.
- No check of data we cannot see. If a period is missing from the export, we say so before calculating. If a whole account is missing, we cannot know.
- No decision on the partial exemption category on your behalf. We classify European funds according to WM Datenservice data; for US funds and closed-end funds you choose the category and carry the justification.
- No MLPs, LPs or royalty trusts. Their distributions are particularly complex for tax purposes; manual rework with a tax advisor is required here.
See for yourself.
Upload your IBKR data and check the preview. Completely free. You only pay when you want to buy the report.