GST AATO Amendment Window for FY 2025-26: 31 July 2026 Checklist for Startup Finance Teams
GSTN issued Advisory No. 666 dated 1 July 2026 on revision of the timeline for amendment of Aggregate Annual Turnover, or AATO, for FY 2025-26. The advisory says the AATO functionality is being upgraded to…
What changed
GSTN issued Advisory No. 666 dated 1 July 2026 on revision of the timeline for amendment of Aggregate Annual Turnover, or AATO, for FY 2025-26. The advisory says the AATO functionality is being upgraded to allow automatic updation as subsequent returns are filed after the amendment window. For FY 2025-26, the taxpayer amendment window has been shifted to 1 July 2026 to 31 July 2026.
The GST portal advisory page is available at https://services.gst.gov.in/services/advisoryandreleases/read/666. ICAI’s GSTN Advisory tracker also lists the 1 July 2026 AATO advisory and the 2 July 2026 e-way bill FAQ update at https://idtc.icai.org/gstn-advisory.php.
For startup finance teams, this is not a cosmetic portal field. AATO can affect GST return behaviour, QRMP eligibility, e-invoicing evaluation, internal compliance review and how external accountants reconcile turnover with financial statements, GST returns and income-tax records.
Who should review AATO before 31 July 2026
| Startup profile | Why review is useful |
|---|---|
| GST-registered SaaS startup | Turnover may include domestic and export supplies differently in internal MIS |
| D2C or marketplace seller | High invoice volume can create mismatch between books and returns |
| Manufacturing or inventory startup | E-way bill and e-invoice thresholds may become relevant |
| Services startup with multiple GSTINs | Entity-level and GSTIN-level turnover must be reconciled carefully |
| Recently funded startup | Investor diligence may compare GST, revenue and financial records |
| QRMP filer | Turnover classification can affect filing frequency choices |
Compliance impact for founders
1. GST return discipline
If AATO is wrong, the finance team may make incorrect assumptions about return filing, compliance monitoring and GST portal alerts. Reconcile AATO with GSTR-1, GSTR-3B, books, credit notes and year-end financials.
2. QRMP and filing frequency
Quarterly Return Monthly Payment eligibility depends on turnover conditions under GST rules. Finance teams should not decide filing rhythm using an unchecked portal figure.
3. E-invoicing readiness
Startups close to e-invoicing thresholds should track AATO carefully. A late discovery creates pressure on ERP, billing, customer communication and tax operations.
4. Investor and lender diligence
Revenue mismatch across GST returns, audited financials, bank statements, invoices and MIS is a common diligence issue. AATO review is a simple way to catch avoidable mismatches.
Documents to keep ready
| Document | Use |
|---|---|
| GSTR-1 and GSTR-3B for FY 2025-26 | Reconcile outward supplies and tax payment |
| GST annual summary | Compare portal turnover with internal totals |
| Sales register | Identify exempt, nil-rated, export and taxable supplies |
| Credit/debit note register | Check turnover adjustments |
| Audited or provisional financials | Match revenue recognition with GST data |
| GSTIN-wise report | Useful for startups with multiple registrations |
| Export invoices and LUT records | Avoid misclassification of export turnover |
| Accountant working paper | Create an audit trail for any amendment request |
Step-by-step checklist before 31 July 2026
- Download GST portal AATO details for FY 2025-26.
- Reconcile GSTIN-wise turnover with GSTR-1 and GSTR-3B.
- Match taxable, exempt, zero-rated and export turnover with books.
- Check credit notes, debit notes, cancellations and year-end adjustments.
- Identify whether amendment is required.
- Keep a working paper approved by the finance owner or external accountant.
- Submit the amendment request on the GST portal before 31 July 2026 if needed.
- Track officer review during 1 August 2026 to 15 August 2026 where applicable.
Mistakes to avoid
- Waiting until 31 July 2026 to reconcile data.
- Checking only total revenue and ignoring GSTIN-wise records.
- Ignoring export, exempt, nil-rated or credit-note treatment.
- Assuming the AATO figure is correct because returns were filed.
- Not documenting why no amendment was needed.
- Failing to align GST turnover with investor data-room revenue schedules.
Sources
- GST portal advisory page for Advisory No. 666: https://services.gst.gov.in/services/advisoryandreleases/read/666
- ICAI GSTN Advisory tracker: https://idtc.icai.org/gstn-advisory.php
- GST portal: https://www.gst.gov.in/
FAQ Section
What is AATO under GST?
AATO means Aggregate Annual Turnover. It is the turnover figure used in several GST compliance contexts and should be reconciled with returns and books.
What is the revised AATO amendment window for FY 2025-26?
The revised taxpayer amendment window for FY 2025-26 is 1 July 2026 to 31 July 2026, based on GSTN Advisory No. 666 dated 1 July 2026.
Who should review AATO?
Every GST-registered startup should review it, especially those near QRMP or e-invoicing thresholds, with multiple GSTINs, exports, high credit-note volume or investor diligence underway.
What happens after the amendment window?
The advisory refers to jurisdictional tax officer review after the taxpayer window. Startups should track the portal and preserve supporting working papers.
Is AATO review only a tax-team issue?
No. It affects founder reporting, investor diligence, ERP readiness, GST compliance planning and finance controls.
Founder / Business Takeaway
AATO review is a small GST task with large downstream value. The Best CS Firm In India lens is to reconcile portal turnover, books and investor-facing numbers before a mismatch becomes a compliance or diligence issue.
Need expert support?
BSA helps startups review GST records, AATO, QRMP eligibility, e-invoicing readiness, GST return reconciliations and investor-ready finance documentation.
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