If you buy shares, you will need to complete a tax return. If you have any doubts or questions over this please take independent financial advice or contact HMRC.
You may have to pay Capital Gains Tax (CGT) if you make a profit when you sell shares. Dabbl will provide a statement to you showing whether you made a "gain" for the tax year. Our fees and any Stamp Duty Reserve Tax incurred will be deducted from profits realised. If your total gains are above your Capital Gains Tax allowance for the tax year, you may well have to pay tax.
For more details see https://www.gov.uk/tax-sell-shares/what-you-pay-it-on
Each year you're allowed to make a certain amount from selling investments for a higher value than you bought them, before you need to pay any tax - for the 2017/18 tax year it's £11,300.
As soon as you realise 'capital gains' above that amount, you'll need to pay CGT. The rate of CGT depends on your level of overall income, including those capital gains. If this total is still within the basic rate band the rate of CGT will be 10%. To the extent that the income and gains are above the basic rate band, it'll be 20%. Tax rates are, of course, subject to change.