If I buy an e-mini futures contract and hold it for several years, rolling it out (i.e. buying and selling the expiring and next contract month in the same transaction) every month before eventually closing it, when do the capital gains become assessable for capital gains tax gains/losses in the UK ? Is it at the end of each tax year on any sales/purchases made exclusively in that tax year. Or is it at the end of the tax year when the trade is finally closed out, based on the final sale price minus the original purchase price several years earlier ? The eventual gain/loss then would be based on a summation of the individual gains/ losses made after each roll.