Add GST
Add GST formula
GST = Base amount × (Rate ÷ 100)
Total = Base amount + GST
Example: ₹10,000 at 18% gives ₹1,800 GST and a total of ₹11,800.
Free India tax tool
GST made clear.
Add or remove GST instantly, with the correct CGST, SGST or IGST split for Indian invoices.
Instant calculation
Choose what you need
Enter the amount before GST.
Amount including GST
₹11,800.00
Base amount
₹10,000.00
GST amount
₹1,800.00
18% GST
CGST
₹900.00
9%
SGST
₹900.00
9%
Total
₹11,800.00
The basics
How GST is calculated
GST is calculated as a percentage of the taxable value of a supply. Add the resulting tax to the base amount to find the invoice total.
For an intrastate supply, the total GST is split equally between CGST and SGST. For an interstate supply, the full amount is shown as IGST.
This tool is for quick calculations and estimates. Use the rate and tax treatment applicable to your specific supply and invoice.
Reverse GST
Reverse GST formula
Base = Inclusive amount ÷ (1 + Rate ÷ 100)
GST = Inclusive amount − Base
Example: ₹11,800 including 18% GST contains ₹10,000 base value and ₹1,800 GST.
Tax components
CGST vs SGST vs IGST
The place of supply determines which components appear on an invoice.
| Component | Used for | At 18% GST |
|---|---|---|
| CGST | Intrastate supply | 9% |
| SGST | Intrastate supply | 9% |
| IGST | Interstate supply | 18% |
Worked examples
GST calculation examples
Add GST · 18%
₹10,000.00
GST: ₹1,800.00
Total: ₹11,800.00
Remove GST · 18%
₹11,800.00
GST: ₹1,800.00
Total: ₹11,800.00
Add GST · 5%
₹2,500.00
GST: ₹125.00
Total: ₹2,625.00
Quick reference
Common GST-rate calculations
Add GST to ₹10,000 to compare common rates.
| GST rate | GST amount | Total amount | CGST + SGST |
|---|---|---|---|
| 5% | ₹500.00 | ₹10,500.00 | 2.5% + 2.5% |
| 12% | ₹1,200.00 | ₹11,200.00 | 6% + 6% |
| 18% | ₹1,800.00 | ₹11,800.00 | 9% + 9% |
| 28% | ₹2,800.00 | ₹12,800.00 | 14% + 14% |
Related GST resources
From calculation to invoicing
Once the tax split is clear, create the document with the free GST invoice generator. Businesses that need saved records, reporting and an ongoing billing workflow can also explore our ready-made business software.
Questions, answered
GST calculator FAQs
How do I add GST to an amount?
Enter the amount before tax, choose Add GST and select the applicable rate. The calculator adds GST to the base amount and shows the total, including the CGST and SGST split or IGST.
How do I calculate GST from an inclusive amount?
Choose Remove GST and enter the amount that already includes tax. The base amount is the inclusive amount divided by 1 plus the GST rate divided by 100.
What is the difference between CGST, SGST and IGST?
CGST and SGST apply together to an intrastate supply, with the GST split equally between the central and state components. IGST applies to an interstate supply as one combined tax amount.
Does the calculator support custom GST rates?
Yes. Along with 5%, 12%, 18% and 28%, you can enter any non-negative custom rate for an estimate.
How accurate is the reverse GST calculation?
The reverse calculation uses the full formula before displaying the result to two decimal places: base amount equals inclusive amount divided by (1 + GST rate ÷ 100).