The Solidarity Surcharge (Soli) is an additional tax levy applied to the amount of the withholding tax (Abgeltungsteuer). For investors, it is typically withheld automatically along with the main tax on investment income.

Although the amount of the surcharge is relatively small, it is part of the overall tax burden on investments in Germany. Therefore, it is useful for investors to take it into account when calculating their portfolio’s net return.