All registered businesses have to file monthly, quarterly and/or annual GST Returns based on the type of business. A return is document containing details of income which taxpayer is required to file with tax administrative authorities. This is used by tax authorities to calculate tax liability. Under GST, a registered dealer has to file GST returns that include: Purchases, sales, output GST, Input tax credit. To file GST returns, GST compliant sales and purchase invoices are required. You can generate GST compliant invoices for free on Clear Tax Billbook. In the GST regime, any regular business has to file three monthly returns and one annual return. This amounts to 37 returns in year.