Capital gains tax

[makingmiracles]

Does anyone know, when calculating capital gains on an investment wether you deduct the original investment amount from the total and then calculate capital gains on just profit?

You get taxed on profits but can you just confirm the nature of the investment.

Valuation - original investment + any previous withdrawals.

Or if it's property, minus original costs purchasing like fees and money spent on improvement but must have receipts etc

So cyptocurrency, say you put in £3k and ended up with £30k, you would work out the tax based on £27k?