If you own 5% or more of stock in a company (for instance a Dutch B.V., a French S.A., a U.K. Ltd. or a U.S. corporation) this share hold is considered substantial. In this case, the benefits you receive from owning the stock are taxable in Box 2 of the Dutch income tax. If you've obtained the 30%-ruling and have the partial non-resident status, only the stock you own in a Dutch company is taxable in Box 2.
The stock that your fiscal partner owns has to be added to the stocks that you personally own to establish if you meet the 5% criteria. You can either be the legal owner of the stock, the economic owner, or both. The 5% can be calculated over the total amount of stocks that a company has, or a specific type of stocks. You could also have options on 5% of the total stock in a company.
If you have a substantial share hold, then all profit distributions you receive are subject to Box 2 taxation. In addition, when you sell part or all of your shares and make a gain, this gain is also taxable in Box 2 of the Dutch income tax. The profit is calculated by subtracting the original price for which you bought the stock from the total revenue from selling the stock. Different rules apply when you sell shares owned prior to moving to the Netherlands.