How reverse GST calculation works
The total you paid is 100% of the base price plus the GST percentage. So the base is the total divided by (100 + rate)%.
Original amount = Total × 100 ÷ (100 + Rate) · GST included = Total − Original amount
| Total paid | Rate | Original amount | GST included |
|---|---|---|---|
| ₹1,050 | 5% | ₹1,000.00 | ₹50.00 |
| ₹1,180 | 18% | ₹1,000.00 | ₹180.00 |
| ₹1,400 | 40% | ₹1,000.00 | ₹400.00 |
| ₹100 | 18% | ₹84.75 | ₹15.25 |
When you need it
- Checking how much input tax credit is inside a purchase bill.
- Setting an all-inclusive price (₹999, ₹4,999) and finding the base to print on the invoice.
- Splitting reimbursements or expense claims into value and tax.
FAQs
Is reverse GST the same as Reverse Charge (RCM)?
No. This tool is reverse arithmetic. Reverse Charge Mechanism is a legal provision where the recipient, not the supplier, pays the GST on certain supplies.
Why doesn’t 18% of the total give the GST?
Because 18% applies to the base, not the total. The GST share of a total at 18% is 18/118 ≈ 15.25%.