GST Calculator

Consumption-tax arithmetic comes in two directions, and mixing them up is the most common billing error there is. Sometimes you have a base price and need tax added on top (₹1,000 + 18% = ₹1,180). Other times you have an all-inclusive total and need the tax extracted from within it — and that is not subtracting the percentage, it is dividing: ₹1,180 ÷ 1.18 = ₹1,000. This calculator handles both directions with a simple Add/Remove toggle.

It is built for more than one country. Pick a tax system and the right presets load: India's GST slabs (5%, 12%, 18%, 28%), UK VAT (0%, 5%, 20%), common EU VAT rates, UAE VAT (0%, 5%), Australia's 10% GST, Singapore's 9%, and Canada's GST/HST tiers — with a custom-rate field for anything else, and the currency switchable independently. For India, the sidebar additionally splits the tax into the intra-state CGST + SGST halves (18% = 9% + 9%) and notes that inter-state supplies charge the full rate as IGST instead — the line items an Indian invoice actually needs.

The reverse direction is the one people genuinely need a tool for: freelancers who quoted "all-inclusive" and must invoice base and tax separately, shoppers checking how much of an MRP is tax, accountants reconciling inclusive receipts. Results are exact to two decimals with a copyable summary, and the disclaimer earns its place: rates and rules change by notification and category — the arithmetic here is exact for the rate you choose, while the right rate for your goods is your accountant's domain. For invoice-ready documents, the Invoice Generator applies these splits automatically.

Adding is multiplication: tax = base × rate ÷ 100, total = base + tax. Removing is division: base = total ÷ (1 + rate ÷ 100), tax = total − base — because the tax was charged on the base, not on the total, subtracting the percentage from the total overstates it (18% of ₹1,180 is ₹212.40, not the correct ₹180).

The regime selector only changes which preset rates are offered, which label the tax carries (GST, VAT, GST/HST), and whether the India-specific split panel appears — the arithmetic is identical everywhere. The CGST/SGST split is the tax halved, matching how intra-state Indian invoices itemize it.

The calculator does price arithmetic for the rate you select — it does not classify goods into slabs, track notifications that change rates, or handle filing concepts like input tax credits and place-of-supply. Preset rates reflect each regime's common slabs and can lag official changes; the custom field covers anything else. The CGST/SGST split assumes the standard equal halves of intra-state Indian supplies. The built-in disclaimer applies: verify the correct rate and filing requirements with your authority or accountant.

Pure client-side arithmetic: add mode computes tax = amount × rate/100; remove mode computes base = amount ÷ (1 + rate/100) with tax as the difference; results display to two decimals with locale-aware currency formatting. The regime table drives preset rate buttons, tax labelling, default currency, and the conditional CGST/SGST split (tax ÷ 2 per component). Custom rates accept 0–100%.

The preset rates per system

Presets cover each regime's common slabs; the custom field takes any other percentage. Rates change by official notification — verify the current rate for your category.

Freelancers and small businesses quoting and invoicing with tax, shoppers and accountants extracting tax from inclusive prices, and anyone working across VAT/GST regimes who wants the right presets at hand. For the full document with line items and automatic splits, the Invoice Generator continues where this leaves off.