As per income tax act, After making the appropriate and permissible intra-head and inter-head adjustments in income of taxable person in computation of total income, there could still be unadjusted losses. These unadjusted losses can be carried forward to future years for adjustments against income of that years. The rules as regards carry forward differ slightly for different heads of income.
A return of loss is required to be furnished for determining the carry forward of such losses, by the due date prescribed for different assessees u/s. 139(1) of the income tax Act.
There is provision regarding calculation of Business profit/loss under head Profit and Gain from business and profession as per Income tax act (not as per books of accounts) If you have a business loss (as per IT act), and you furnished the return of loss within a due date of furnishing return, claimed the losses in that year than only loss can be carried forward to next year.