Self-declaring as a DEGIRO or Interactive Brokers investor: a walkthrough

Why this walkthrough exists

DEGIRO and Interactive Brokers are established outside Belgium, so they are not part of the Belgian withholding system. Everything they leave untaxed is still owed — it simply becomes yours to declare. This page walks through the three returns that receive those amounts and, for each, the document that supplies the figures. It describes the mechanics; it does not tell you what to trade or how to structure a portfolio, and it is not a substitute for the official instructions or professional advice. Confirm the current forms and deadlines on MyMinfin.

The three obligations, and where each is filed

A self-declaring investor typically faces three separate filings:

1. TOB — the tax on each buy and sell, filed monthly.
2. Foreign dividends — the 30% Belgian withholding on distributions the broker did not withhold, filed in the annual return.
3. Realised capital gains — the 10% tax on gains realised from 2026, filed in the annual return.

They are separate returns with separate deadlines, so it helps to treat them one at a time.

Step 1 — TOB, from your trade confirmations

Every executed order carries TOB. Because the broker did not withhold it, you file it yourself:

• Gather the trade confirmations for the period. Each shows the transaction value, which is the TOB base.
• Apply the rate that matches the instrument — 0.12%, 0.35% or 1.32% — and the per-transaction cap where it bites.
• Submit the total through the monthly TOB declaration on MyMinfin, by the deadline for the month the trades settled in.

The document that feeds this step is the broker's transaction history or contract-note export.

Step 2 — Foreign dividends, in the annual return

Distributions the broker paid you without Belgian withholding go into the annual return:

• Take the gross foreign dividend and the foreign withholding already applied from the broker's dividend report.
• The 30% Belgian tax is settled in the return; any treaty credit for the foreign withholding is claimed in the same place.
• Keep the dividend report — it is the evidence for both the gross amount and the foreign tax already paid.

The document that feeds this step is the broker's annual dividend statement.

Step 3 — Realised gains, in the annual return

Since 2026, gains you realise are taxed at 10%. The measurement is what takes care:

• For positions held on 31 December 2025, the gain is measured from the step-up value on that date, not your original purchase price.
• For positions opened afterwards, the gain is measured from actual cost, matched lot by lot.
• Losses and the annual exemption enter the same calculation before the 10% applies.

The document that feeds this step is the broker's realised-gains or activity statement — but it reports the raw sale, not the Belgian step-up-adjusted gain, which is the piece you reconstruct.

Where the documents don't line up with the return

A foreign broker's statement is organised around your trades, not around Belgian tax lines. The gross figures are all there, but the mapping — this sale into the capital-gains line, this dividend into the dividend line with its foreign credit, these transactions into the TOB total — is the work left to you.

Belfolio reads the DEGIRO or Interactive Brokers export and produces those three totals in the shape the returns expect, including the 31 December 2025 step-up where it applies. It reports the figures; the decision to file them, and the confirmation that they match your own records, stays with you. Always check the output against your source documents before submitting anything.

An order can be priced ahead of time with the stock exchange tax simulator; what postponing the TOB filing costs, the penalty simulator shows.