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Quantity and Tax Calculator

Three quick calculators for invoice lines: quantity × rate with discount and GST, taxable value with charges, and a discount-and-tax comparison.

After the GST rate rationalisation effective 22 September 2025, the main slabs are 5% and 18%, with 40% for specified goods. 12% and 28% are kept here for reference and older documents. Always check the current rate for your item on CBIC GST.

Discount and tax breakdown

See how a discount given on the invoice changes the taxable value, the GST and the amount the buyer pays.

	No discount	With discount
List price	₹2,000.00	₹2,000.00
Discount	₹0.00	− ₹200.00
Taxable value	₹2,000.00	₹1,800.00
GST @ 5%	₹100.00	₹90.00
Buyer pays	₹2,100.00	₹1,890.00

Buyer saves ₹210.00 in total, of which ₹10.00 is lower GST.

How it works

Each invoice line follows the same order: quantity × rate gives the gross amount, the discount is deducted to get the taxable value, and GST is applied on the taxable value. Within a state the tax is split equally into CGST and SGST/UTGST; for inter-state supplies it is IGST.

Formulas

Gross = Quantity × Rate per unit
Discount = Gross × Discount % ÷ 100
Taxable value = Gross − Discount (+ packing, freight and other charges billed)
GST = Taxable value × GST rate ÷ 100; Line total = Taxable value + GST

Example (illustrative)

A Surat textile wholesaler bills 25 metres at ₹480 per metre with 5% discount, GST at 5%, to a buyer in the same state.

Gross (25 × ₹480)	₹12,000.00
Discount @ 5%	− ₹600.00
Taxable value	₹11,400.00
CGST @ 2.5% + SGST @ 2.5%	₹285.00 + ₹285.00
Line total	₹11,970.00

Frequently asked questions

Is freight charged on the invoice part of the taxable value?

Generally yes. Incidental expenses such as packing and freight charged by the supplier to the buyer are included in the value of supply under Section 15 of the CGST Act. Check the conditions for your case.

Does a discount reduce GST?

A discount recorded in the invoice at or before the time of supply generally reduces the taxable value, and therefore the GST. Post-supply discounts have extra conditions. The calculator only shows the arithmetic.

How many decimals can I use for quantity?

Up to three decimals, which suits units like kilograms, metres or litres. Amounts accept up to two decimals.

How is the line total rounded?

Each step is rounded to the nearest paisa: gross, discount, then each tax component. Invoice-level rounding to the rupee is available in the invoice generator.

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