Someone did mention paying 30% earlier as capital gains tax ITT. This tax is applied to most types of 'incomes' that are not derived from traditional employement/business practices. Whether you need to pay taxes on your bitcoin depends on whether or not you've made a profit. If you were to convert capital (SEK for example) to Bitcoin and then purchase something the very same day for that same amount, you obviously won't pay any taxes because you haven't made a profit.

But, whether you pay for something or hold your bitcoin as they increase in value is irrelevant as it all comes down to how much your capital has appreciated over the year, at the end of which you'll pay the 30% tax gains on the increase/profits (not on the total amount of your capital).

That said, there's also the prescription time to take into consideration, I believe taxation debts are prescribed after five years and counting, so let's say you made an income from investing in bitcoin and assume your assets are undiscovered for six years, the gains you make that first year should at least be prescribed (forgiven), but you'd still have to pay five years retrospectively and this assumes that you're not reported and investigated at some point.

I'm not entirely sure about the above, but I believe that might be how it works to an extent at least.