Invoices, receipts and price tags often show only the final price. To extract GST from total amount figures like these, you need to work backwards and split each total into the price before tax and the GST included in it. It takes one division, but most people get it wrong the first time.
Price before GST = Total ÷ (1 + rate ÷ 100)
Worked example: take GST out of 1,180 at 18%
- Price before GST = 1,180 ÷ 1.18 = 1,000.
- GST included = 1,180 − 1,000 = 180.
- Check: 1,000 + 18% = 1,180. ✔
In India, intra-state GST is split equally into CGST and SGST, so 180 becomes 90 CGST + 90 SGST. For inter-state sales the whole 180 is IGST.
The common mistake
Many people simply take 18% of the total: 18% of 1,180 is 212.40, which is wrong. GST is charged on the price before tax, not on the total, so you must divide, not multiply. The same applies at any rate: 10% of 1,100 is 110, but the GST inside 1,100 at 10% is only 100.
Shortcuts for common GST rates
| GST rate | GST in the total | Price before GST |
|---|---|---|
| 5% | Total × 5 ÷ 105 (or ÷ 21) | Total ÷ 1.05 |
| 10% (e.g. Australia) | Total ÷ 11 | Total ÷ 1.10 |
| 12% | Total × 12 ÷ 112 | Total ÷ 1.12 |
| 15% (e.g. New Zealand) | Total × 3 ÷ 23 | Total ÷ 1.15 |
| 18% | Total × 18 ÷ 118 | Total ÷ 1.18 |
| 28% | Total × 28 ÷ 128 | Total ÷ 1.28 |
Examples: extracting GST from common totals
| Total incl. GST | 5% GST | 12% GST | 18% GST | 28% GST |
|---|---|---|---|---|
| 1,000 | GST 47.62 · net 952.38 | GST 107.14 · net 892.86 | GST 152.54 · net 847.46 | GST 218.75 · net 781.25 |
| 2,360 | GST 112.38 · net 2,247.62 | GST 252.86 · net 2,107.14 | GST 360 · net 2,000 | GST 516.25 · net 1,843.75 |
| 3,500 | GST 166.67 · net 3,333.33 | GST 375 · net 3,125 | GST 533.90 · net 2,966.10 | GST 765.62 · net 2,734.38 |
| 5,000 | GST 238.10 · net 4,761.90 | GST 535.71 · net 4,464.29 | GST 762.71 · net 4,237.29 | GST 1,093.75 · net 3,906.25 |
| 10,000 | GST 476.19 · net 9,523.81 | GST 1,071.43 · net 8,928.57 | GST 1,525.42 · net 8,474.58 | GST 2,187.50 · net 7,812.50 |
India's GST reform from 22 September 2025 moved most goods and services into two main slabs, 5% and 18%, with a 40% rate for certain luxury and sin goods. Older invoices can still show 12% or 28%, so they are included above.
Adding GST vs including GST
- GST exclusive (add GST): you have the price before tax. Total = Price × (1 + rate ÷ 100). 1,000 + 18% = 1,180.
- GST inclusive (extract GST): you have the final total. Price = Total ÷ (1 + rate ÷ 100). 1,180 incl. 18% = 1,000 + 180 GST.
If you are not sure which one applies, look at the invoice: "inclusive of all taxes" means GST is already in the total.
Calculate GST online in one step
Our free GST calculator does both directions. Set Calculation to "Remove GST from a Total", enter the amount and the rate, and it shows the price before tax and the GST instantly, with the CGST/SGST split explained, for any currency. For other percentage maths, such as a mark-up or a discount on a GST price, try the percentage calculator or the discount calculator.
Calculators used in this guide
Extract gst from total amount – FAQs
How do I extract GST from a total amount?
Divide the total by (1 + rate ÷ 100) to get the price before GST, then subtract it from the total. At 18%, 1,180 ÷ 1.18 = 1,000, so the GST is 180.
What is the formula for GST inclusive calculation?
GST included = Total × rate ÷ (100 + rate). For 18%, that is Total × 18 ÷ 118.
How do I take GST out of a total at 10%?
Divide the total by 11. For example, 1,100 ÷ 11 = 100 GST, leaving 1,000 before tax.
Why is 18% of the total not the GST?
Because GST is charged on the price before tax. 18% of 1,180 is 212.40, but the GST included in 1,180 is only 180.
Further reading: Goods and Services Tax, India (Wikipedia) · GST rate of 9% (IRAS Singapore)