GST Reverse Calculator

Calculator

Calculation mode

Use reverse mode when you only know the final, tax-included total.

Total amount (GST included)

Tip: you can paste values with commas.

GST rate (%)

Common rates: 0, 5, 12, 18, 28.

Tax type

Choose IGST for inter-state supply; otherwise split tax.

Currency symbol

Used for display and exports only.

Rounding

Rounding can change the split cents slightly.

Reset

Educational tool only. Check local GST rules and invoice requirements.

Example data table

Total (incl.)	GST rate	Base (pre-tax)	GST amount	Notes
₹ 1,180.00	18%	₹ 1,000.00	₹ 180.00	Common retail invoice
₹ 1,050.00	5%	₹ 1,000.00	₹ 50.00	Reduced-rate goods
₹ 560.00	12%	₹ 500.00	₹ 60.00	Mid-rate supplies

Numbers shown assume reverse mode and nearest 2-decimal rounding.

Formula used

Let r be the GST rate in percent.

Reverse (total includes GST):
Base = Total ÷ (1 + r/100)

GST = Total − Base
Forward (base excludes GST):
GST = Base × (r/100)

Total = Base + GST
Splits:
IGST = GST

CGST = GST/2, SGST = GST/2

If your jurisdiction uses different components or rules, adjust accordingly.

How to use this calculator

Select Inclusive → Exclusive to reverse from a tax-included total.
Enter the amount and the GST rate shown on the invoice.
Pick IGST or CGST + SGST depending on the supply type.
Choose rounding to match your billing policy.
Press Submit to view base, GST, and split values.
Use Download CSV or Download PDF for records.

FAQs

1) What does “GST reverse” mean?

It means calculating the pre-tax base value when you only know the final amount that already includes GST. The calculator separates the tax portion and shows a clean breakdown.

2) Which amount should I enter in reverse mode?

Enter the total you paid or charged, including GST. The tool divides by (1 + r/100) to recover the base and then subtracts to get GST.

3) When should I choose IGST?

Choose IGST when the supply is treated as inter-state or when your invoice shows a single GST component. Otherwise, select CGST + SGST for an equal split display.

4) Why do CGST and SGST sometimes differ by a cent?

Rounding can create tiny differences. The calculator rounds each component and then adjusts one side slightly so the two components add up to the GST total.

5) Can I use custom GST rates?

Yes. Enter any rate from 0 upward. If you use unusual rates, keep consistent rounding so your invoice totals match your accounting policy.

6) Does this replace professional tax advice?

No. It is a math helper for estimating splits and reverse values. Always follow your local rules for what must appear on invoices and how taxes should be reported.

7) What is “effective rate” in the result?

Effective rate is the GST portion divided by the base amount, expressed as a percent. It should closely match the entered rate, with small differences possible due to rounding.

8) Where is my calculation history stored?

History is stored only in your current session to show recent results on this page. Closing the browser or clearing session data will remove it.