What triggers Sec 270(1) (old Sec 143(1)) demand: (1) AIS shows income not declared in ITR, most common. (2) TDS in Form 168 (old Form 26AS) not matching claimed TDS in ITR. (3) Deduction claimed exceeds limit. (4) Arithmetical mistake in ITR. (5) Carried-forward loss claimed without filing return in loss year. Three possible Sec 270(1) (old Sec 143(1)) outcomes: (A) Refund, CPC agrees with your return, issues refund. (B) No demand, no refund, CPC processing matches your return. (C) Demand, CPC finds discrepancy, raises a demand. Do NOT just pay the demand: Sec 270(1) (old Sec 143(1)) demands are often incorrect. In the most common case, FD interest in AIS that taxpayer forgot to declare, the demand is valid but the penalty is avoidable. In the second most common case, TDS credit mismatch due to PAN error by employer, demand is incorrect and should be rectified. Response options: (A) Agree, pay demand.