For each trade you have specific income and specific tax deductible expenses associated with that income and your net is your profit or loss as you all well know. Broadly, if your activities fall within the same sort of income type, or schedules as they're called, you can offset losses (deficit in terms of taxable income less taxable expenses) from one trade against another for the year in which they occur. you can't do the same for brought forward and carried forward losses as they can only be offset against the trade in which they were realised. Again, it all depends on what it is you're doing.