GST Calculator

GST (Goods and Services Tax) is the single destination-based indirect tax that India levies on the supply of most goods and services. Since 1 July 2017 it has replaced the older tangle of VAT, service tax, central excise, octroi and entry tax with one unified structure. This calculator does the two jobs every shopkeeper, freelancer, small-business owner and salaried buyer needs: it adds GST to a pre-tax price to find what you should charge or pay, and it removes GST from a tax-inclusive total to find the underlying base value — and it splits the tax into CGST + SGST or IGST automatically.

Who is this for?

Traders and GST-registered businesses raising tax invoices, freelancers and consultants billing clients, e-commerce sellers reconciling payouts, and ordinary shoppers who want to know how much of an MRP is actually tax. If you file GSTR-1 or GSTR-3B, the add/remove split here mirrors the lines you report.

The GST rate slabs

GST has four main slabs — 5%, 12%, 18% and 28% — plus special rates of 0% (nil-rated essentials), 0.25% (rough diamonds and precious stones) and 3% (gold, silver and jewellery). The 18% slab is the workhorse, covering most services and a large share of goods. Demerit and luxury items in the 28% slab often attract an additional compensation cess on top — this calculator computes the GST itself; any product-specific cess must be added separately.

How it works — the exact formulas

Adding GST (forward). When you know the base (pre-tax) price:

GST Amount = Base Price × Rate ÷ 100

Final Price = Base Price + GST Amount

Removing GST (reverse). When you only have the GST-inclusive total and need to back out the base — common with MRP, gross receipts or invoices that show one figure:

Base Price = Final Price × 100 ÷ (100 + Rate)

GST Amount = Final Price − Base Price

CGST + SGST vs IGST

The place of supply decides how the same total tax is labelled. For an intra-state supply (buyer and seller in the same state, e.g. a Pune seller billing a Pune client), the tax is split equally — half is Central GST (CGST), half is State GST (SGST). So an 18% slab appears as 9% CGST + 9% SGST. For an inter-state supply (across state lines, or an import), a single Integrated GST (IGST) is charged at the full rate and later apportioned between the Centre and the destination state. The total tax is identical either way — only the split changes.

Worked example (₹)

Say a Mumbai design studio bills a Mumbai client ₹10,000 for a service taxed at 18% (an intra-state supply). GST = 10,000 × 18 ÷ 100 = ₹1,800, so the invoice total is 10,000 + 1,800 = ₹11,800. Because it is intra-state, the ₹1,800 shows as ₹900 CGST + ₹900 SGST. If the same client were in Gujarat, the invoice would instead show a single ₹1,800 IGST line. Now reverse it: a retail bill shows ₹11,800 inclusive of 18% GST. The base is 11,800 × 100 ÷ 118 = ₹10,000 and the embedded GST is 11,800 − 10,000 = ₹1,800.

Key tips

• Use Remove GST whenever a figure is already tax-inclusive (MRP, gross sales). Adding GST to an inclusive amount double-counts the tax.
• Match the slab to the correct HSN/SAC code of your product or service — the rate is driven by the code, not by guesswork.
• For the 28% slab, check whether a separate compensation cess applies and add it on top.
• Registered businesses can usually claim Input Tax Credit (ITC) on GST paid for business inputs, reducing net tax payable — track it separately.

Common mistakes

• Splitting IGST into CGST + SGST (or vice-versa) — the split depends entirely on intra- vs inter-state place of supply.
• Applying reverse GST with Final × Rate ÷ 100 instead of Final × 100 ÷ (100 + Rate) — a frequent over-statement of the base.
• Assuming everything is 18% — staples can be 5%, jewellery 3%, and many essentials are 0%.

India notes

GST registration is generally mandatory once turnover crosses ₹40 lakh for goods or ₹20 lakh for services (lower thresholds apply in special-category states). Slabs and cess are set by the GST Council and revised from time to time, so always confirm the current rate for your HSN/SAC against an authoritative source such as gst.gov.in before filing. This tool is for estimation and learning — it is not a substitute for professional GST advice.