Tax arithmetic • Add or remove GST
GST Calculator
Add GST to a taxable value or extract the GST component from an inclusive amount. Choose an intra-state or inter-state display for a simple mathematical tax split.
Enter amount and rate
Use base value in Add mode and final GST-inclusive value in Remove mode.
Common values are suggestions only. Verify the current applicable rate.
Formulas
Add mode: GST = base × rate ÷ 100
Final price = base + GST
Remove mode: base = inclusive ÷ (1 + rate ÷ 100)
GST component = inclusive − base
What this tool cannot decide
- HSN/SAC classification.
- Whether a supply is exempt or zero-rated.
- Place-of-supply treatment.
- Input-tax-credit eligibility.
- Registration or return-filing obligations.
Add and remove example
For a ₹10,000 taxable value at 18%, GST is ₹1,800 and the final price is ₹11,800. Removing 18% from ₹11,800 returns the same values, subject to rounding.
| Mode | Taxable value | GST | Final value |
|---|---|---|---|
| Add 18% | ₹10,000 | ₹1,800 | ₹11,800 |
| Remove 18% | ₹10,000 | ₹1,800 | ₹11,800 |
In the intra-state illustration, ₹1,800 is displayed as ₹900 CGST and ₹900 SGST. In the inter-state illustration, it is displayed as ₹1,800 IGST.
Common mistakes
- Subtracting the rate directly from an inclusive price.
- Assuming a common rate applies to every supply.
- Confusing zero-rated with exempt treatment.
- Using a tax split without checking place-of-supply rules.
- Treating arithmetic as filing advice.
Invoice review checklist
- Confirm taxable value and quantity.
- Verify current classification and rate.
- Check supplier and recipient details.
- Review state codes and place of supply.
- Retain invoice and supporting records.
Related calculators and guides
Frequently asked questions
How do I add GST?
Multiply base value by the rate and add the GST.
How do I remove GST?
Divide the inclusive amount by one plus the decimal rate.
Why not subtract 18%?
GST was calculated on the smaller base value.
Does this identify the correct rate?
No.
How is CGST and SGST shown?
The tool splits total GST equally for the intra-state illustration.
How is IGST shown?
The full GST amount is displayed as IGST.
Does it calculate input tax credit?
No.
Can I file from this result?
No; it is arithmetic only.
Educational disclaimer
This calculator provides mathematical GST estimates, not tax, classification, legal or filing advice. Verify the applicable rate, supply treatment and current official requirements before acting.