What is a GST Calculator?
GST (Goods and Services Tax) is India’s unified indirect tax, charged as a percentage of the transaction value at the applicable slab rate for that good or service. Following the GST 2.0 rate rationalisation, most goods and services now fall under a simplified 5% or 18% structure, with a 40% rate reserved for select luxury and "sin" goods.
Switch between adding GST to a base price (exclusive) or extracting the base amount from a price that already includes GST (inclusive) — the two calculations aren’t just mirror images of each other, so it’s easy to get wrong by hand.
How each mode is calculated
In inclusive mode, dividing (not simply subtracting the percentage) is what correctly reverses out the GST, since the rate was originally applied to the smaller base amount, not the larger inclusive one.
Worked example: the naive-subtraction mistake, in rupees
Take a GST-inclusive price of ₹11,800 at 18%. The correct base amount, found by dividing by 1.18, is exactly ₹10,000, with ₹1,800 as the GST component. The common mistake — subtracting 18% of ₹11,800 directly — gives ₹11,800 − ₹2,124 = ₹9,676, which understates the true base by ₹324. That gap exists because the 18% was originally calculated on ₹10,000, not on the larger ₹11,800 figure, so subtracting 18% of the wrong (larger) number always overshoots.
Reading a price as "plus GST" vs. "inclusive of GST"
"₹1,000 plus GST" means ₹1,000 is the base — use exclusive mode, and the customer pays ₹1,000 × 1.18 = ₹1,180 at 18%. "₹1,000 inclusive of GST" means ₹1,000 already contains the tax — use inclusive mode, and the actual base is only about ₹847.46, with roughly ₹152.54 being GST. The two phrasings look similar but describe different starting points, and using the wrong mode for a given quote is a common, easily-avoided billing error.
Frequently asked questions
What are the current GST slabs?
Following the GST 2.0 reform, the main slabs are 0% (exempt items) and two standard rates of 5% and 18%, with a special 40% rate for select luxury and sin goods — down from the earlier four-slab structure. Always check the applicable rate for your specific good or service, since exceptions exist.
Why can’t I just subtract 18% to remove GST from an inclusive price?
Because 18% was calculated on the smaller base amount, not on the larger GST-inclusive total — subtracting 18% of the inclusive price removes too much. Dividing by (1 + rate) is the correct way to reverse it.
Does this calculate CGST and SGST separately?
No — it shows the total GST amount. For an intra-state sale, that total is typically split evenly into CGST and SGST (half each); for an inter-state sale, the full amount is charged as IGST.
Is GST charged on the MRP or a discounted price?
GST is charged on the actual transaction (selling) price after any discount is applied, not on the printed MRP — if a shop discounts a ₹1,000 MRP item to ₹800, GST is calculated on ₹800.
Do all goods and services use the same GST rate?
No — the rate depends on the specific HSN (goods) or SAC (services) classification. Essential items are often exempt or taxed at 5%, most goods and services fall under 18%, and select luxury or sin goods attract 40%. This calculator lets you enter any applicable rate directly.
Can a business claim back the GST it pays on purchases?
Yes, registered businesses can generally claim Input Tax Credit (ITC) for GST paid on business purchases, offsetting it against GST collected on sales — this calculator computes the GST amount itself, not the downstream ITC treatment.
Is GST included in the price shown to consumers?
For most retail transactions, yes — the displayed price is expected to be inclusive of GST, per India’s pricing display norms, which is why the inclusive (extract GST) mode is often the more commonly needed one for everyday shopping-related calculations.