Rate of income-tax: framework for charging tax including aggregation of agricultural income and surcharge application. Income-tax is chargeable at rates in the First Schedule with specified surcharges; separate Parts prescribe rates for deduction at source and advance tax. Where net agricultural income exceeds a de minimis and total income passes thresholds, agricultural income is aggregated with total income to compute tax, then tax on an increased agricultural income is subtracted and the balance increased by a surcharge. Chapter XII and certain Act sections provide alternative rate mechanisms. The section defines key terms used in applying the Schedule.