The section numbers all changed.
Here is where yours went.

What actually changed

Very little of the tax, and almost all of the citation. The 2025 Act is a re-write for simplification: rates, thresholds, eligibility conditions and deadlines carry over close to intact, while the structure consolidates hard. Roughly 1,200 provisos and 900 explanations are absorbed or dropped, and the rules follow — 511 rules and 399 forms become a draft 333 rules and 190 forms.

The Act also retires the “previous year” and “assessment year” pair in favour of a single tax year (section 3). Section 536(3) provides that a reference to a tax year is read as a reference to the corresponding previous year under the old Act, which is what keeps old proceedings coherent.

TDS is the disruptive part

Around forty TDS sections — the 194-series along with 193, 195, the 196-series and 197A — collapse into Chapter XIX-B, sections 392 to 402, and almost every deduction obligation now sits inside a table in section 393. There is no section “194J” or “194C” left to cite.

• 393(1) — payments to residents, by table serial.
• 393(2) — payments to non-residents (old 195 is Sl. No. 17).
• 393(3) — payments to any person irrespective of residence (winnings, cash withdrawal, partner payments).
• 393(4) — the exemptions and carve-outs.
• 394 — all of TCS, in one table. 395 — lower/nil deduction certificates. 397 — TAN and no-PAN penal rates. 398 — assessee-in-default consequences.

Citations that will trip people up

• 197 used to mean the lower-deduction certificate. Under the 2025 Act it means long-term capital gains; the certificate is section 395.
• 37 used to mean the general business deduction. Under the 2025 Act it means actual-payment deductions (old 43B); the general deduction is section 34.
• HRA, LTC and the other Chapter III exemptions are no longer sections at all — they move into Schedule III, read with section 11(1).
• 115BAC becomes 202. Every payroll system and Form 16 template that hardcodes the old number needs a change.

Where this page is honest about not knowing

• The CBDT's own 'Utility to check provisions of Income-tax Act, 1961 vis-a-vis Income-tax Act, 2025' exists and its URL was located, but incometaxindia.gov.in returns HTTP 403 to automated fetching, so no row here is sourced from the government utility itself. A human should spot-check high-stakes rows against it directly in a browser.
• The official CBDT 'FAQs on Interplay and Transition to the Income-tax Act, 2025' PDF also returned HTTP 403. The transition rule stated on this page is sourced from incometax.gov.in's 'Objective and scope of the New Act' page plus secondary reporting of the department's clarification, not from the FAQ PDF itself.
• The primary text used is the Income-tax Act, 2025 AS PASSED (ICAI publication dated 8 September 2025). A version 'AS AMENDED BY FINANCE ACT, 2026' exists but could not be fetched. Any rate or threshold amended by the Finance Act, 2026 is therefore NOT reflected in the notes. Section numbers are unaffected; rates and thresholds must be re-checked against the FA 2026 text before use.
• Form numbers are deliberately excluded. Secondary sources report 24Q to 138, 26Q to 140, 27Q to 144, 15G/15H to a single Form 121, and 3CA/3CB/3CD to Form 26 — but the Draft Income-tax Rules, 2026 are not yet finally notified and these are indicative only.
• TDS challan and return payment codes are also excluded. They come from a single specialist secondary source and could not be corroborated against a CBDT notification. They matter operationally — verify before configuring any TDS filing system.
• Where old provisions were consolidated many-to-one, the reverse mapping is lossy. Section 19 absorbs old 16 plus 10(10), 10(10A), 10(10AA), 10(10B) and 10(10C); s.393 absorbs roughly 40 old sections; s.206 absorbs the entire MAT/AMT block; s.532 absorbs faceless-scheme powers from seventeen old sections. Anyone relying on a one-to-one lookup for these should read the destination section in full.
• The '~1,200 provisos and ~900 explanations removed' and '~40% volume reduction' figures come from secondary summaries and were not independently verified. The 536 sections / 16 schedules versus 819 sections / 14 schedules counts ARE from the official incometax.gov.in page and are reliable.
• Widely-circulated commentary tables do contain errors. One otherwise-accurate concordance article states '45 to 80', which contradicts both the ICAI concordance and the text of s.67 itself (45 to 67). Every row marked 'confirmed' here was checked against the statutory text, not just against commentary.

Frequently asked

• ICAI Direct Taxes Committee — Income Tax Act, 2025, including tabular mapping vis-a-vis the 1961 Act →

  Primary source (8 September 2025, 818 pp). Contains both the complete 2025-to-1961 concordance table and the full bare text of the Income-tax Act, 2025, used to verify section content, sub-section numbers and table serial numbers directly.

• Income Tax Department — Objective and scope of the New Act →

  Official confirmation of 536 sections / 16 schedules versus 819 sections / 14 schedules, the 01.04.2026 repeal date, the rules and forms reduction, and the s.536(3) transitional reading of 'tax year'.

• CBDT — Utility to check provisions of Income-tax Act, 1961 vis-a-vis Income-tax Act, 2025 →

  The government's own correspondence utility. Located but not machine-readable (HTTP 403). Open it in a browser to spot-check anything high-stakes.

• CBDT — FAQs on Interplay and Transition to the Income-tax Act, 2025 →

  Official transition FAQ. Located but not machine-readable (HTTP 403).

• CBDT — Income-tax Act, 2025 as amended by the Finance Act, 2026 →

  The post-Finance-Act-2026 bare Act. Located but not machine-readable (HTTP 403). Relevant for any rate or threshold check.