Key points
- Cut over at the start of a month so one GSTR-1 period isn't split across two systems' reports, or plan to combine them.
- Move four things: party masters, item masters with HSN and rates, opening balances, and open (unpaid) bills party by party.
- Clean before you move: inactive GSTINs, 4-digit HSN codes where 6 are needed, and wrong state codes cause IRP rejections later.[1][2]
- Invoice numbers must stay consecutive, unique for the financial year and at most 16 characters (rule 46).[3]
- Keep old records for 72 months from the annual return due date (section 36).[4]
Step 1: plan the cut-over
- Date: the first day of a month, after closing the previous month's billing. The first day of a quarter or of the financial year is even cleaner.
- People: one owner for the move (usually the accountant), your CA, and one person from the billing counter.
- What stays behind: closed bills of earlier years stay in the old system as records; only balances and open bills move.
- Freeze: no master edits in the old system after the export.
Step 2: clean masters before you export
| Check | Why it matters | How |
|---|---|---|
| Every B2B party's GSTIN is valid and active | Inactive GSTINs are rejected by the IRP (error 3029)[1] | Check each GSTIN; mark cancelled ones as unregistered |
| State code matches the GSTIN's first two digits | Mismatch is rejected (error 2265)[1] | Fix the party's state |
| HSN has 6 digits if turnover is above ₹5 crore | Required on invoices; invalid HSN is rejected (2176)[1][2] | Update item HSN codes |
| GST rate per item is current | Rates changed from 22 Sep 2025[5] | Update rates with effective dates |
| No duplicate parties | Split balances, double reminders | Merge duplicates in the old system first |
Step 3: export from your current software
Most billing and accounting software can export ledgers, items and outstanding bills to Excel. You need: party list with GSTIN, address, state, credit period and opening balance; item list with HSN, unit, rate and GST rate; and bill-wise outstanding for every party.
If you are moving from Tally
In TallyPrime, Tally's help pages describe the export like this:[6]
- Press Alt+E (Export) and choose Masters. Press C (Configure), set the type of master (accounting or inventory), turn on Include dependent masters, and, if you want, Export closing balance as opening balance. Choose the format (Excel or XML) and press E.
- For transactions, press Alt+E, choose Transactions, configure the voucher type and period, and export.
- For open bills, export the outstanding reports (for example Bills Receivable or ledger outstandings) from Alt+E → Others.
Step 4: import and check
Import masters first, then balances, then open bills. Before anyone bills, check these totals against the old system on the cut-over date:
Reconciliation checks
- Number of parties and items matches the export.
- Total receivables and total payables match, to the rupee.
- Top 20 parties' bill-wise outstanding matches, bill by bill.
- Stock quantity and value of the top 50 items match.
- Every flagged GSTIN, state code and HSN issue is fixed or consciously accepted.
Step 5: keep invoice numbering legal
Rule 46(b) requires a consecutive serial number, in one or more series, at most 16 characters, using letters, numbers, hyphen or slash, and unique for the financial year.[3] Two safe ways across a switch:
- Continue the same series: if the old system's last bill was NG/26-27/1842, the new one starts at NG/26-27/1843.
- Start a new series with a different prefix, for example NGC/26-27/0001, and report both series in GSTR-1's documents-issued table for that period.
Don't reuse a number that already has an IRN: the IRP rejects it as a duplicate (error 2150).[1]
Step 6: run side by side, then switch off
For the first few days, bill only in the new system but keep the old one open for lookups. Check that e-invoices and e-way bills come through, that reminders go to the right numbers, and that your CA can see everything. Then make the old system read-only. Keep it, or its full export, for 72 months from the due date of the annual return for each year it holds.[4]
Worked example
Kulkarni Electricals, Nagpur (sample firm) switches on 1 November 2026, after billing October in its old desktop software.
| Item | Old system | New system | Status |
|---|---|---|---|
| Parties | 412 | 412 | Match |
| Items | 1,850 | 1,850 | Match |
| Total receivables | ₹1,12,40,000 | ₹1,12,40,000 | Match |
| Total payables | ₹38,75,500 | ₹38,75,500 | Match |
| GSTINs flagged | 2 cancelled | Marked unregistered | |
| HSN codes flagged | 18 with 4 digits | Updated to 6 digits | |
| Last invoice number | KE/26-27/2210 | Next: KE/26-27/2211 | Series continues |
October's GSTR-1 comes entirely from the old system; November's entirely from the new one, so no period is split. The CA exports November vouchers to the books as before.
How Moharbill helps
- Imports from Tally exports or Excel: parties with GSTINs checked, items with HSN codes, opening balances and open bills. See integrations.
- Flags inactive GSTINs, wrong state codes, 4-digit HSN codes and duplicate parties before you bill.
- Continues your invoice series from your last number, and exports vouchers to Tally if your CA keeps the books there.
- Free GSTIN check and HSN finder for cleaning masters.
Frequently asked questions
What data should I move to new billing software?
Party masters, item masters with HSN and GST rates, opening balances, and every open (unpaid) bill party by party. Closed bills of past years can stay in the old system as records.
When is the best time to switch billing software?
At the start of a month, after closing the previous month's billing, so that one GSTR-1 period does not come from two systems. The start of a quarter or financial year is even cleaner.
Can I continue my invoice numbers in the new software?
Yes. Rule 46 requires consecutive numbers unique for the financial year, up to 16 characters. Continue the same series or start a new series with a different prefix, and report all series in GSTR-1.
How do I export masters from Tally?
In TallyPrime, press Alt+E, choose Masters, press C to configure (type of master, include dependent masters, closing balance as opening), choose Excel or XML, and press E.
How long must I keep the old software's data?
Section 36 of the CGST Act requires records to be kept for 72 months from the due date of the annual return for the year they relate to.
Sources
All read on 17 Oct 2026.
- NIC e-invoice portal, Resolution for Common Errors (2150, 2176, 2265, 3029). einvoice1.gst.gov.in
- NIC e-invoice portal notice on 6-digit HSN (Notification 78/2020-CT). einvoice1.gst.gov.in
- CGST Rules 2017, rule 46(b), CBIC. taxinformation.cbic.gov.in
- CGST Act 2017, section 36, CBIC. taxinformation.cbic.gov.in
- PIB, "Recommendations of the 56th Meeting of the GST Council", 3 Sep 2025. gstcouncil.gov.in
- Tally Solutions help, "How to Export Data in TallyPrime". help.tallysolutions.com
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