GST Calculator

What does this GST Calculator do?

GST (Goods and Services Tax) is added to the price of most goods and services at standard slab rates. This calculator works in both directions: adding GST to a base price ("exclusive" mode) or extracting the base price and GST amount from a total that already includes tax ("inclusive" mode).

The formulas

Adding GST (exclusive → inclusive): GST amount = base × rate ÷ 100; Total = base + GST amount.

Removing GST (inclusive → exclusive): Base amount = total ÷ (1 + rate ÷ 100); GST amount = total − base.

Step-by-step example

For a ₹10,000 item at 18% GST (exclusive mode): GST = 10,000 × 18 ÷ 100 = ₹1,800. Total price = ₹11,800.

Now suppose a bill already shows ₹11,800 as the final, GST-inclusive amount, and you want to find the base price: base = 11,800 ÷ 1.18 = ₹10,000 — confirming the GST portion was ₹1,800.

Tips & common mistakes

• Don't simply subtract the GST percentage from an inclusive total (e.g., 11,800 − 18% ≠ the correct base price) — you must divide by (1 + rate/100), not multiply by (1 − rate/100).
• Always confirm which GST slab applies to your specific goods or service (5%, 12%, 18%, or 28%) before calculating — rates vary significantly by category.
• Keep exclusive and inclusive amounts clearly labeled on invoices — mixing them up is a common bookkeeping error.

Why businesses need both directions of this calculation

Businesses issuing invoices typically need to add GST to a base price to determine the customer-facing total. But businesses reconciling expenses, or consumers trying to understand what portion of a receipt was tax versus the actual cost of goods, need to go the other direction — extracting the base price and tax amount from an already-inclusive total. This calculator handles both directions because both are common real-world needs, not just one.

GST slabs and why rates differ by category

Goods and Services Tax is applied at different rates depending on the category of goods or service — commonly 5%, 12%, 18%, or 28% in systems that use this slab structure, with some essential goods at 0% and certain luxury or "sin" goods carrying additional cess on top of the highest slab. Because the applicable rate varies so much by category, always confirm the correct rate for your specific product or service rather than assuming a default.

More tips

• When reading an invoice, check whether the listed price is described as "inclusive of GST" or "exclusive of GST" — this single word changes which formula applies and the mistake is easy to make when scanning quickly.
• For B2B transactions, GST paid on business purchases ("input tax credit") can typically be offset against GST collected on sales — a detail well outside what this calculator covers, but relevant context if you're doing this math for actual business accounting.

Frequently asked questions