What DA-1 is trying to solve
Foreign dividends may arrive after tax has already been withheld in the source country. A Swiss resident then still reports income and wealth in Switzerland. DA-1 is commonly used in the workflow for crediting eligible foreign withholding taxes.
This is a different topic from Swiss anticipatory tax. The Swiss 35% rule applies to certain Swiss-source income. DA-1 is about foreign tax withheld before money reaches your Swiss-resident tax file.
The practical point is simple: if your portfolio contains foreign dividend-paying securities, keep the tax trail from the start. Waiting until the return is due makes DA-1 much harder.
Why the broker statement matters
The tax office or tax software needs more than a screenshot of your portfolio. You need year-end positions, dividend income, source-country withholding, currency data, and security identifiers that can be matched to official tax values where relevant.
ICTax is useful because Swiss tax reporting often needs security-level information, not only a portfolio total. A broker that exports clean statements can save time even if its trading fee is not the lowest.
If the broker report hides withholding tax, mixes currencies, or gives only monthly cash movements, you may still be able to file, but the admin burden shifts to you or your adviser.
A safe DA-1 workflow
First, separate Swiss-source withholding from foreign-source withholding. Second, list every foreign dividend by country, security, gross income, tax withheld, and broker document.
Third, check whether the treaty and Swiss filing route support a credit or refund position. Do not assume that the full foreign withholding is always recoverable. Source-country rules and treaty limits can change the result.
Fourth, store the final filed forms with the broker statements. If you change broker, leave Switzerland, or receive a tax office question later, the history will be readable.
For small portfolios, the value of DA-1 may be modest. For larger dividend portfolios, poor documentation can become expensive, especially when several countries and currencies are involved.