How to Calculate GST (Add or Remove It From a Price)

To calculate GST, open the GST Calculator, set Mode to Add GST or Remove GST (inclusive), enter the amount and pick a GST rate %, and read the result instantly — along with the CGST and SGST halves of that GST amount.

What the GST Calculator does

GST math splits into two directions, and they aren't mirror images of each other. If you have a price before GST, adding tax is simple multiplication. But if you only have a GST-inclusive amount — a bill total, a price tag that already includes tax — pulling the GST back out isn't the same calculation run in reverse; dividing by 1 + rate/100 gives a different (correct) answer than just subtracting the rate. The GST Calculator handles both: Add GST takes an amount excluding GST and a rate, and gives you the GST and the amount including GST; Remove GST (inclusive) takes a GST-inclusive amount and a rate, and gives you the GST and the amount excluding GST. Either way, it also splits the GST amount evenly into CGST and SGST — the central and state halves used for GST on sales within the same state in India's GST system.

How to calculate GST with Toolbench

1. Open the GST Calculator.
2. Set Mode to Add GST if you're starting from a price that doesn't yet include GST, or Remove GST (inclusive) if your amount already has GST baked in.
3. Enter the amount. The field is labeled Amount excl. GST in Add mode, or Amount incl. GST in Remove mode.
4. Pick GST rate % from the standard slabs: 5%, 10%, 12%, 15%, 18% or 28%.
5. In Add mode, read Amount incl. GST as the main result, with Net amount, GST, Gross amount, CGST and SGST shown below it.
6. In Remove mode, read Amount excl. GST as the main result, with the same breakdown rows below it.
7. Click any value to copy it, or use Copy results to copy everything as plain text.

Example: adding GST to a price

The tool opens in Add mode with Amount excl. GST 1000 and GST rate % 18:

Mode	Add GST
Amount excl. GST	1,000
GST rate %	18%
Amount incl. GST	1,180.00
Net amount	1,000.00
GST (18%)	180.00
Gross amount	1,180.00
CGST (9%)	90.00
SGST (9%)	90.00

18% of 1,000 is 180.00 in GST, split evenly into 90.00 CGST and 90.00 SGST, for a GST-inclusive amount of 1,180.00.

Example: removing GST from a total

Switch to Remove GST (inclusive) with an amount of 5,000 and a GST rate of 12%:

Mode	Remove GST (inclusive)
Amount incl. GST	5,000
GST rate %	12%
Amount excl. GST	4,464.29
Net amount	4,464.29
GST (12%)	535.71
Gross amount	5,000.00
CGST (6%)	267.86
SGST (6%)	267.86

Dividing 5,000 by 1.12 (not multiplying 5,000 by 12%) gives the pre-GST amount of 4,464.29. The GST itself, 535.71, is the difference between the GST-inclusive amount and that pre-GST amount — not 12% of 5,000, which would overstate it.

Why you can't just take a percentage of the total

Starting point	Wrong approach	Wrong result	Correct result
Incl.-GST amount 5,000, rate 12%	12% of 5,000 subtracted from 5,000	4,400.00	4,464.29
Incl.-GST amount 1,180, rate 18%	18% of 1,180 subtracted from 1,180	967.60	1,000.00

The rate was applied to the smaller, pre-GST amount in the first place, so taking that same percentage of the larger GST-inclusive total removes too much. Dividing the inclusive amount by 1 + rate/100 reverses it correctly — which is exactly what Remove GST (inclusive) mode does.

GST rate slabs available

Rate	Typical use
5%	Common for essential goods
10%	Available slab
12%	Common for standard-rated goods
15%	Available slab
18%	Common for most goods and services
28%	Common for luxury and sin goods

These are the six rate options in the calculator's GST rate % dropdown. Actual rates depend on the goods or services involved — check current GST schedules for your category rather than assuming one.

Tips and common mistakes

• Pick the right mode first. If your number is a quoted price or cost before tax, use Add GST. If it's a bill, invoice, or receipt total that already has GST in it, use Remove GST (inclusive).
• Don't take a percentage of the inclusive total to remove GST. As the table above shows, that removes too much. Divide by 1 + rate/100 instead — or let the calculator do it.
• CGST and SGST are each half the GST rate. The calculator's split assumes a sale within the same state; inter-state GST (IGST) isn't calculated here.
• GST rates vary by category of goods or services. Pick the slab that matches what you're actually calculating GST on.

Related tools

• Sales Tax Calculator — add or back tax out of a price using any custom tax rate, not fixed slabs.
• Percentage Calculator — percent of, percent change, increase and decrease.
• Discount Calculator — sale price after one or two stacked discounts, with optional tax.
• Margin Calculator — profit margin and markup from cost and price.

Frequently asked questions

How do I calculate GST on a price?

Multiply the pre-GST amount by the GST rate as a decimal (rate ÷ 100) to get the GST amount, then add that to the original amount. The GST Calculator's Add GST mode does this and also shows the CGST and SGST halves.

How do I remove GST from a total that already includes it?

Divide the GST-inclusive amount by 1 + rate/100. For example, a 5,000 inclusive amount at a 12% GST rate works out to 4,464.29 before GST. Subtracting 12% of 5,000 instead gives the wrong answer.

What's the difference between CGST and SGST?

They're the two halves of GST charged on a sale within the same state in India's GST system — each is exactly half the total GST rate. A sale between different states uses IGST instead, which this calculator doesn't compute.

Does the GST Calculator support custom GST rates?

No. It offers a fixed dropdown of standard slabs: 5%, 10%, 12%, 15%, 18% and 28%. For an arbitrary tax rate, use the Sales Tax Calculator, which accepts any rate you type in.

Is my data sent to a server when I use the GST Calculator?

No. The calculation happens in your browser as you type. If you're signed in, your inputs sync privately to your account; if you're signed out, nothing is saved anywhere.