Hi Dominic, I am currently living in Paris but I am originally from the Netherlands (I used to live in Leiden where I studied for my bachelor's degree). I am curious to know what broker you are planning to use in the Netherlands (as most of them let European customers pay by traded value which is horrible). The only broker that seemed OK to me is SpeedTrader (even though PDT-rules apply).
I think the Dutch tax system is quite nice for retail traders. In the Netherlands there are basically three categories of income, each with their own rules and tax rates (we call them 'boxes', so there is 'box 1', 'box 2' and 'box 3'); and gains made by retail day traders fall into 'box 3'. In general 'box 3' corresponds to savings and investments but in 2011 the Supreme Court of the Netherlands decided that day trading activities, due to its speculative character, should also be placed in this category. Effectively this means that there is a very low flat tax on your gains.
Before 2017 one needed to pay 1.2% over the gains (more specifically, one needed to pay 30% tax on a fixed assumed yield of 4% of the value of the assets). They have changed this system very recently but the rates and percentages are still on the low side. Details can be found on the website of the 'Dutch IRS': https://www.belastingdienst.nl/wps/wcm/connect/bldcontentnl/belastingdienst/prive/vermogen_en_aanmerkelijk_belang/vermogen/belasting_betalen_over_uw_vermogen/grondslag_sparen_en_beleggen/berekenen_belasting_over_uw_inkomsten_uit_vermogen_vanaf_2017/berekenen_belasting_over_uw_inkomsten_uit_vermogen_vanaf_2017. (Unfortunately, this is written in Dutch so probably you would need someone to help you out.)
Anyhow, good luck in Amsterdam, and feel free to write me back.
-- Ammar
