The gross total income is the income earned by an individual under the various heads of income in a financial year. To compute gross total income, one just has to add the income from various sources. It includes all the income from house rent, business, salary or capital gains. The taxable income can be computed by deducting the applicable income tax deductions from the gross total income. If you have made certain investments that qualify for income tax deductions, just subtract the permissible limit of deduction from the gross total income to get the taxable income.