Box 3 is considered as an unclear and unfair element in the Dutch income tax system, which has been subject to a lot of discussion. Below we listed a simplified history of the Box 3 tax system (taxation of savings and investments) - starting in 2017,  when a revised system was implemented up to late 2024, where the Dutch tax authorities started sending letters in which they offer taxpayers the possibility to provide your actual result from investments. 

Note that this 'in a nutshell' version does not contain details that may be very relevant in specific situations.

As per 2017, a low deemed result rate was determined for cash and savings and a high deemed result rate for all other investments. A certain tax free amount in wealth applied and the deemed rates were applied to the excess wealth. Next a three bracket scheme was in place where the ratio savings (low result) versus investments (high result) changed in each bracket and the deemed result from investment progressively grew with the value of the wealth on January 1 of the concerning tax year. 

On December 24, 2021 the Surpreme Court decided that the 2017 Box 3 method was contrary to the right of ownership and the prohibition of discrimination. The Surpreme Court decided that the actual result should be considered rather than a deemed result.  

The Dutch tax authorities came up with a fix in which the high and low result rates (which are annually adjusted) would still apply, but where these would be applied to the actual ration cash/savings versus investments.

This fix was diverted into the revised Box 3 method in the Dutch Tax Act as per 2023.

On June 6, 2024 however, the Surpreme Court decided that the revised 2023 method was in some situations still a violation of human rights and that for investments. The deemed investment income still could lead to very undesirable situations. Again the Surpreme Court decided that the actual result from investments should be considered if the actual result is less than the deemed (based on the determined high result rate for investments) result.
 
Providing actual result from investments
The Dutch tax authorities currently offer the possibility to provide details on actual result from investments. 

The actual data can be provided in your personal profile on the website of the Dutch tax authorities (which you can access with Digid). 

Note that for the actual income, there is no tax free amount. All direct income from investments (rental income, dividends, interest on obligations) is considered as taxable income as well as the (un)capitalized gain/loss on investments in the concerning tax year (so the increase/decrease in value). 

More information on the "Opgaaf werkelijk rendement" can be found here.