If my sell value is lower than Cost (or indexed or inflation adjusted cost), I have a loss rather than income. It is allowed to remember (carry forward) this loss and adjust against any future capital gains I may have in next 8 years, but to get this right, I must file my tax return for the year in which I had loss on the due date of return (not stretching it to the last date of return). But my long term loss can be adjusted only against long term gains I have.
Further I can’t adjust my capital gains loss against other incomes, such as salaries, house property or the like.