How GST Is Calculated
Adding GST (you know the pre-tax price): GST = Base × Rate ÷ 100, then Total = Base + GST. A ₹1,000 service at 18% becomes ₹1,180.
Removing GST (the price already includes tax): Base = Inclusive × 100 ÷ (100 + Rate). A ₹1,180 bill at 18% contains ₹180 GST on a ₹1,000 base. The common mistake is subtracting 18% of ₹1,180 (₹212.40) — that over-removes, because the 18% was charged on the base, not the total.
Working out your margin after tax? Pair this with our Percentage Calculator or Discount Calculator. Estimating annual tax instead? See the Income Tax Calculator.
Quick Reference: 18% GST on Common Amounts
| Base price | GST @18% | Total | If total includes GST, base is |
|---|
| ₹500 | ₹90 | ₹590 | ₹423.73 |
| ₹1,000 | ₹180 | ₹1,180 | ₹847.46 |
| ₹5,000 | ₹900 | ₹5,900 | ₹4,237.29 |
| ₹10,000 | ₹1,800 | ₹11,800 | ₹8,474.58 |
| ₹1,00,000 | ₹18,000 | ₹1,18,000 | ₹84,745.76 |
The last column is the trap most people fall into: a ₹10,000 bill that includes GST does not contain ₹1,800 of tax — it contains ₹1,525.42, because the 18% was charged on the smaller base. The same formulas work for any VAT/sales-tax country — just change the rate.
Frequently Asked Questions
How do I calculate GST on a price?
To add GST: GST amount = Base × Rate ÷ 100, Total = Base + GST. ₹1,000 at 18% → ₹180 GST, ₹1,180 total.
How do I remove GST from an inclusive price?
Base = Inclusive × 100 ÷ (100 + Rate). ₹1,180 including 18% GST → ₹1,000 base + ₹180 GST. Use "Remove GST" mode above.
What are CGST and SGST?
For intra-state sales, GST splits equally: 18% = 9% CGST (central) + 9% SGST (state). Inter-state sales use IGST at the full rate.
What are the GST slab rates?
Main slabs: 5%, 12%, 18% (most common) and 28%. Some goods are 0%/exempt. Enter any custom rate above — the quick buttons cover the four main slabs.
How much is 18% GST on ₹10,000?
₹1,800, making the total ₹11,800. If ₹10,000 already includes GST, the base is ₹8,474.58 and tax is ₹1,525.42.
Can I use this for VAT or sales tax in other countries?
Yes — the math is identical for any percentage tax (UK 20% VAT, UAE 5% VAT…). Type the rate in the custom box; only the CGST/SGST split is India-specific.