legal ground
Article 4 of the Provisional Regulations of People's Republic of China (PRC) on Value-added Tax.
Except as provided in Article 11 of these Regulations, the taxable amount of taxpayers selling goods, labor services, services, intangible assets and real estate (hereinafter referred to as taxable sales) is the balance after deducting the current input tax from the current output tax. Calculation formula of tax payable: tax payable = current output tax-current input tax.
When the current output tax is less than the current input tax, the insufficient part can be carried forward to the next period for further deduction.