BRSR Core Assurance in 2026: What the Top 500 Expansion Means for Your Company

India's compliance calendar is unusually crowded this month. Entities under the Carbon Credit Trading Scheme are finalising verified emissions reports ahead of the scheme's first compliance milestone, and a separate, less-discussed deadline is closing in on a much larger group of companies: BRSR Core reasonable assurance. For FY2025-26, SEBI's glide path pulls in the top 500 listed entities by market capitalisation, nearly double the previous year's cohort. If your company sat just outside the top 250 last year but has since moved up in rank, this may be the first year mandatory assurance applies to you, and lenders and institutional investors are increasingly asking for the assurance certificate itself, not just the underlying numbers.

What Changed for FY2025-26

SEBI introduced the BRSR Core framework through its July 12, 2023 circular, phasing in mandatory reasonable assurance on a fixed schedule rather than applying it to every listed company at once. The glide path runs:

• FY2023-24: Top 150 listed entities by market capitalisation

• FY2024-25: Top 250 listed entities

• FY2025-26: Top 500 listed entities

• FY2026-27: Top 1,000 listed entities

For companies newly crossing into the top 500, whether through market cap growth, index reclassification or a recent listing, FY2025-26 is the first year reasonable assurance on BRSR Core stops being optional. Ranking is assessed as of the SEBI-specified reference date each year, so a company that was comfortably outside scope twelve months ago can find itself newly covered without any change in its own reporting practices. Unlike the rest of the BRSR report, which is largely self-reported, the nine BRSR Core KPIs now need a third-party assurance opinion attached before filing.

Reasonable Assurance Is a Higher Bar Than Most Teams Expect

Companies that have only encountered limited assurance, the lighter standard used for value chain disclosures, sometimes assume BRSR Core assurance works the same way. It doesn't. Reasonable assurance requires extensive testing, larger sample sizes, an evaluation of internal control effectiveness, and a positive opinion from the provider, closer in rigour to a financial statement audit than a light review. The assurance provider must also be genuinely independent: neither the firm nor its associates can sell products or provide non-assurance services, including consulting, to the company or its group entities in the same cycle. That rules out using one firm for both ESG advisory and BRSR Core assurance simultaneously. Where the provider cannot get comfortable with the evidence trail behind a KPI, the result is a qualified or adverse opinion attached to a public filing, which is precisely the outcome most sustainability and investor relations teams are trying to avoid.

The Nine KPIs Under the Assurance Lens

Assurance applies specifically to the nine BRSR Core attributes, spanning all three ESG pillars:

• Greenhouse gas footprint (Scope 1 and Scope 2 emissions)

• Energy consumption, split between renewable and non-renewable sources

• Water withdrawal and consumption intensity

• Waste generated and how it is managed

• Gender diversity across the workforce and leadership

• Wage parity between men and women at comparable levels

• Employment of differently-abled persons

• Share of inputs sourced from ESG-assessed suppliers

• Open and fair engagement with customers, including complaint handling

Each figure needs a defensible measurement boundary, a consistent methodology, and an audit trail an outside provider can independently test, not a number assembled in the final week of the reporting cycle.

A Readiness Checklist Before the Deadline

BRSR filings, including the Core assurance opinion, are generally due within 150 days of fiscal year-end, around the last week of August for companies on an April-March cycle. That leaves a narrow runway once the reference-date ranking is out, particularly for a company assembling assurance-ready evidence for the first time. Companies newly in scope this year should:

1. Confirm your market capitalisation ranking as of the SEBI-specified reference date to verify whether you now fall inside the top 500

2. Map data ownership for each of the nine KPIs across finance, HR, EHS and procurement before requesting sign-off from any single function

3. Engage an independent assurance provider early, since capacity tightens sharply as the deadline approaches

4. Run an internal dry-run review to catch evidence and documentation gaps before the external assurance process begins

5. Cross-check BRSR Core figures against related disclosures, including CBAM and CCTS filings, for consistency, since auditors and regulators increasingly compare numbers across frameworks

Teams filing for the first time may find it useful to start from our 90-day roadmap for first-time BRSR filers, which maps the same groundwork against a tighter clock, or our deep dive into the nine BRSR Core KPIs for how each metric is actually measured.

Moving from self-reported to independently assured ESG data is a process change, not just a documentation exercise, and it goes more smoothly with a head start than a scramble. If your company has crossed into the top 500 this year, or you simply want a gap assessment before assurance begins, Csquare's ESG reporting team can help you build a BRSR Core-ready data framework and get your evidence trail in order well before auditors arrive. Get in touch to schedule a readiness review before the August deadline.