Glossary
What is a tax period?
The month or quarter a GST return covers, and therefore the window every invoice date falls into.
Updated
In short
A tax period is the month or quarter a GST return covers. SimpleERP's sales and purchase registers filter by any date range, so each tax period's totals come straight from your posted invoices and bills.
A tax period under GST is the period for which a return is filed. For most taxpayers it is a calendar month: GSTR-1 and GSTR-3B are filed monthly. Small taxpayers with aggregate turnover up to ₹5 crore may opt for the QRMP scheme, filing quarterly returns while paying tax monthly. The annual return covers the financial year from April to March.
Tax period: a worked example
Lakshmi Steel Furnitures files monthly. Its September 2026 tax period:
| Item | September 2026 |
|---|---|
| Sales, taxable value | ₹3,39,400 |
| Output GST at 18% | ₹61,092 |
| ITC from purchases of ₹1,73,300 | ₹31,194 |
| Tax payable in cash | ₹29,898 |
| GSTR-1 due | 11 October 2026 |
| GSTR-3B due | 20 October 2026 |
FAQ
Questions, answered
Should I file monthly or quarterly?
If your aggregate turnover is up to ₹5 crore you may choose QRMP and file GSTR-1 and GSTR-3B quarterly, paying tax monthly. Monthly filing gets your B2B buyers their credit sooner. Ask your accountant which suits your customers.
What are the usual due dates?
For monthly filers, GSTR-1 is due on the 11th and GSTR-3B on the 20th of the next month. Under QRMP, the quarterly GSTR-3B is due on the 22nd or 24th depending on the state. Dates can be extended by notification; check the GST portal.
Can I change a sale after the period is filed?
A sale in a filed period cannot be changed by editing it. Correct it through a credit note or debit note in a later period, or an amendment in GSTR-1. In SimpleERP posted invoices cannot be edited, and a lock date can close a filed period entirely.
What is a lock date for?
A lock date stops anyone posting or cancelling documents dated on or before it. Set it after you file a tax period, so the registers you filed from always match the books. In SimpleERP the database enforces it.
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