I find it very easy if done within an ISK. You pay a tax of 30% of the state borrowing rate ( ca 1.5 % rate on long Swedish bond) on the total account value.
http://www.investeringssparkonto.se
In 2018 this works out at 0.45% of the total account value. After paying that you get to keep all other gains without further tax. No writing off loses either though. Just pay 0.45% of account total and that is it for the year.
When I last did the numbers it is lower tax than US and UK. No tax tax forms or trades to report either as brokers send account details to tax agency.
Anyone else in Sweden ?