GST Changes From 1 April 2026: New Rules, Limits & What Your Business Must Do

Every year the new-FY GST checklist gets longer, and every year someone bills their first April export without a live LUT. I am Manoj, ERPNext and Frappe implementation lead at MithTech in Bengaluru. What follows is the cutover runbook we walk our own clients through each March.

Which changes hit your business?

One turnover figure and four toggles. The checker maps your profile onto every April 2026 change and ranks what needs attention first.

What does the full change list cover?

Most of the GST changes April 2026 activates are annual rituals with new enforcement attached. Two are genuinely new teeth. The table is the whole post in one scan:

Sources for the statutory items: ClearTax's April 2026 roundup, Treelife's amendment note on the refund-threshold removal, and Kanakkupillai's FY 2026-27 summary on the annual-return blocker. Verify the fine print against CBIC notifications with your CA — this post is a runbook, not a legal opinion.

Why is the annual-return a blocker?

This is the change that reorders your March priorities. Late fees on GSTR-9/9C for FY 2025-26 are computed by the portal and accrue daily — no more filing a year late for a flat fee. Worse, a pending annual return blocks FY 2026-27 GSTR-3B filings outright. Miss it and your April 3B does not go through. Blocked 3Bs cascade: unfiled 3Bs suspend e-way bill generation, and your customers watch their GSTR-2B for your invoices in vain. One overdue annual return becomes a company-wide operations problem in about six weeks.

ERPNext's side of this is preparation, not filing. The india_compliance app ships GSTR-1 export and a GSTR-3B report (india_compliance/gst_india/doctype/gstr_1/ and gstr_3b_report/, checked at v16.6.0). Its Purchase Reconciliation Tool (purchase_reconciliation_tool/) handles the 2B-vs-books matching that GSTR-9 preparation feeds on. If your reconciliation is current month-to-month, the annual return is an assembly job. If it is not, start now — our GST return filing guide covers the monthly cycle that makes March boring.

What does the rate settlement mean?

Nothing changes on rates on 1 April — that already happened. The 0/5/18/40 slab structure has been in force since September 2025, and the tobacco compensation cess ended in February 2026 with products moving to 18% or 40%. April's job is an audit. Item tax templates, price lists and POS configurations were patched in a hurry last September — recheck them systematically before the new FY's contracts renew. In ERPNext that is a filtered Item Tax Template list and an afternoon — not a project.

How does the document series reset work?

Rule 46(b) wants a fresh, unique invoice series each financial year. What ERPNext actually does is more precise than most explanations of it — and worth understanding, because the wrong pattern is compliant but ugly and the right one is automatic.

The mechanism, from Frappe's own source (frappe/model/naming.py, checked against v16 at ERPNext 16.28.0). The series counter lives in a Series table keyed on the resolved prefix — the docstring at line 428 spells it out:

# frappe/model/naming.py:428 (revert_series_if_last docstring)
"""
* key is naming series          - SINV-.YYYY-.####
* name is actual name           - SINV-2021-0001

1. This function split the key into two parts prefix (SINV-YYYY)
   & hashes (####).
2. Use prefix to get the current index of that naming series
   from Series table
"""

Date tokens resolve at document-creation time (elif e == "YYYY" at line 368). So SINV-.YYYY.-.#### became SINV-2026-0001 on 1 January and will not reset on 1 April — the calendar token flips in January. Numbers stay unique within the FY, so it is defensible; it is also two number blocks per FY and noisier GSTR-1 reconciliation. The clean pattern is an FY-encoded prefix — SINV-2627-.#####. — created fresh each year and switched as the DocType default on 1 April. The counter restarts at 1 automatically, because a new prefix is a new row in the Series table. No renumbering, no manual counter edits.

What does the cutover checklist cover?

Eleven items, grouped by who they apply to. Tick them off — the March order matters, and the annual return goes first.

Three items deserve their week in March rather than a slot on 31 March. The annual return — the blocker above makes it a hard dependency for April. The LUT — the GST portal does not queue nicely on 31 March evenings. A zero-rated invoice without a live LUT means paying IGST and chasing a refund. And the e-invoice sweep — if FY 2025-26 closed above ₹5 crore, you need IRP credentials, configuration and a sandbox round-trip before the first April invoice. The full applicability logic, exemption list and liability-date finder are in our e-invoice limit guide; the operational 30-day and 24-hour windows are in the deadlines post.

What happens to sales bills and accounts?

The recurring failure here is ownership, not knowledge. Billing teams change invoice series when told. Nobody tells them, because the LUT, the declarations and the annual return live in different heads. The split that works:

• Accounts owns the calendar: annual return, LUT filing, CMP-02/QRMP windows, GTA declaration collection. Each gets a named owner and a date in the first week of March — not "March".
• Billing owns the switch: new series live from the first April document, zero-rated invoices checked against the LUT field, no old-series stragglers. The client-script gate below makes this mechanical.
• One custom field bridges them: custom_lut_valid_upto on Company, maintained by accounts, enforced at billing time. The same pattern as the AATO field from the e-invoice watcher — small shared state, loudly enforced.

How do you automate the cutover?

Four recipes: a billing-time gate, a March countdown, its packaged variant, and the 1 April smoke test that tells you the switch worked before your first real invoice does.

// Client Script · DocType: Sales Invoice · Apply To: Form
// Two gates for the first week of April:
// 1) old-FY series must not carry into FY 2026-27 documents
// 2) zero-rated invoices need a live LUT (kept on a Company custom
//    field: custom_lut_valid_upto, maintained by accounts)

frappe.ui.form.on("Sales Invoice", {
    validate(frm) {
        const pd = frm.doc.posting_date || "";
        const inNewFy = pd >= "2026-04-01";

        if (inNewFy && /2526/.test(frm.doc.naming_series || "")) {
            frappe.throw(
                "This invoice uses the FY 2025-26 series. Rule 46(b) needs a " +
                "fresh series for FY 2026-27 - switch the naming series " +
                "before submitting."
            );
        }

        const zeroRated = ["SEZ", "Overseas"].includes(frm.doc.gst_category);
        if (inNewFy && zeroRated) {
            frappe.db.get_value("Company", frm.doc.company, "custom_lut_valid_upto")
                .then((r) => {
                    const upto = (r.message && r.message.custom_lut_valid_upto) || "";
                    if (!upto || upto < pd) {
                        frappe.throw(
                            "No live LUT on record for " + frm.doc.company +
                            " (valid up to: " + (upto || "never filed") + "). " +
                            "File the FY 2026-27 LUT before zero-rated billing."
                        );
                    }
                });
        }
    },
});

What should your new-FY policy cover?

GST FY-Cutover Policy (draft — for CA / auditor review): The FY cutover is owned by the finance controller and executed against a written checklist each March. GSTR-9/9C for the closing FY is filed by 15 March. The LUT for the incoming FY is filed by 20 March; no zero-rated invoice is raised in the new FY without a live LUT on record. New FY-prefixed document series are created by 25 March and switched as defaults at close of business 31 March, with the drafts queue cleared the same day. GTA forward-charge declarations are collected by 15 April; freight bills from undeclared GTAs are booked under reverse charge until a declaration arrives. AATO is recomputed at FY close and checked against the ₹5 crore and ₹10 crore lines; e-invoicing configuration changes only with the controller's sign-off. The 1 April smoke test must pass before billing opens. Ratify the dates with your CA — a December-year-end group or a heavy exporter should pull every date earlier.

Do now or schedule for March

FAQ: what do people ask most?

What is the GTA declaration and do I need one?. Goods Transport Agencies can opt to charge GST under forward charge instead of you paying under reverse charge. The option is exercised per financial year, so each GTA you use should give you a written declaration for FY 2026-27. Without it, book their bills under reverse charge until one arrives.

Which ERPNext version does this post apply to?. Code citations are from Frappe/ERPNext v16.28.0 with india_compliance v16.6.0. The naming-series mechanism is identical in v14 and v15. The statutory deadlines are software-independent — they apply whatever system you bill from.

What related issues might you hit?

• The e-invoice limit and liability dates — the ₹5 crore rule this post's sweep enforces, with the exemption list and threshold watcher.
• The 30-day and 24-hour e-invoice windows — the operational deadlines for everyone above ₹10 crore.
• GST return filing from ERPNext — the monthly GSTR-1/3B cycle that makes the annual return an assembly job.

What should you do next?

None of the April 2026 changes is difficult on its own. Their cost is concentration: eight small deadlines landing in the same fortnight, owned by different people, with a filing blocker waiting for whoever forgets the big one. Put the checklist in your tracker, the gates in your instance, and the smoke test on 1 April morning. The ERPNext implementation side of this is a day of configuration — the fire-drill version in mid-April is a month of unwinding.