TAN format: 4 letters (city code + entity initial) + 5 digits + 1 letter check digit. So `BLRR12345A` indicates Bangalore region.
Who needs TAN: any business deducting TDS — paying salary above ₹15K/month, contractor payments, professional fees, rent above ₹50K, commission. Apply via Form 49B; takes 5-10 days. Failure to apply but deducting TDS = penalty under Section 272BB.
TAN is used in TDS challan, quarterly TDS returns (24Q for salary, 26Q for non-salary, 27EQ for TCS), and Form 16/16A issued to deductees. Keep TAN distinct from PAN — different IDs, different purposes.