How to use this GST calculator
This GST calculator handles both directions of the GST maths — forward (add GST to a base amount) and reverse (extract GST from an inclusive MRP). Four inputs drive the result:
- Amount — either the pre-GST base price (for forward mode) or the GST-inclusive total (for reverse mode). The GST calculator handles both with the same field — you pick the mode via the toggle.
- GST rate — pick from CBIC standard slabs (0% / 0.25% / 3% / 5% / 12% / 18% / 28%) or enter a custom rate for items with specific state / slab overrides. The GST calculator defaults to 18% since it covers most services and B2B supplies.
- Supply type — intra-state splits into CGST + SGST (each at half the rate); inter-state rolls up into full IGST. The GST calculator auto-fills the split in the result.
- Cess + discount (optional) — compensation cess for 28%-slab items (tobacco, aerated drinks, luxury cars) and trade discount to reduce taxable value before GST. The GST calculator applies discount first, then GST on the net.
Every input auto-saves to the URL — useful if you’re a freelancer generating multiple invoices, a retailer comparing MRP vs supply-price, or an accountant reconciling input tax credit. Share the URL with a CA or client to show exactly how the GST number was calculated.
How the GST calculator works
India’s Goods and Services Tax (GST) replaced a tangle of central and state indirect taxes in July 2017. Every domestic supply now attracts a single combined rate that splits between Central GST (CGST) and State GST (SGST) for sales within the same state, or rolls up into Integrated GST (IGST) for sales that cross state lines. This calculator does both directions of the maths—adding GST to a base amount (forward / exclusive) or extracting GST from an MRP (reverse / inclusive)—at every standard CBIC rate.
Standard GST rates (FY 2026-27)
- 0% — exempt: fresh produce, milk, books, education, healthcare
- 0.25% — rough diamonds (HSN 7102)
- 3% — gold, silver, jewellery (HSN 7108-7114)
- 5% — essentials, branded grain, small restaurants, footwear < ₹1,000
- 12% — processed food, business-class air travel, some textiles
- 18% — the standard rate covering most services and B2B supplies
- 28% — luxury and sin goods: cars, ACs > 1.5 ton, cement, tobacco, aerated drinks
A handful of 28% goods also attract an additional compensation cess of 1%–290% for very high-tax items like chewing tobacco and pan masala. This calculator’s “cess (%)” field lets you add it on top of the base rate when needed.
Composition scheme
Small dealers below ₹1.5 crore turnover (₹50 lakh for services) can opt for the composition scheme: a flat tax on turnover with no input tax credit. Three rates apply:
- 1% — traders and manufacturers
- 5% — restaurants
- 6% — service providers (turnover ≤ ₹50L)
Forward (exclusive) calculation
When a vendor quotes a base price and you need to know the final invoice value, use the forward mode:
Total payable = base + (base × rate / 100)
Example: a software invoice of ₹1,00,000 at 18% GST attracts ₹18,000 of GST and totals ₹1,18,000. For an intra-state supply that splits as ₹9,000 CGST + ₹9,000 SGST. For an inter-state supply, the full ₹18,000 is charged as IGST.
Reverse (inclusive) calculation
When you have the MRP or final invoice value and need to back out the base and the GST component (useful for input-tax-credit working, accounting reconciliation, or comparing pre-GST and post-GST quotes):
Base = gross / (1 + rate / 100) GST = gross − base
Example: an MRP of ₹1,18,000 inclusive of 18% GST gives a base of ₹1,00,000 and GST of ₹18,000. Round-tripping forward then reverse recovers the original base to within ₹1 (the only drift is rupee rounding at each step).
Intra-state vs inter-state
The split between CGST and SGST is purely a tax-administration concern (collected centrally then shared with states); the customer pays the same amount either way. The choice depends on the “place of supply” rules under Sections 10–13 of the IGST Act:
- Intra-state — supplier and recipient in the same state → CGST + SGST, each at half the headline rate.
- Inter-state — supplier and recipient in different states (or imports / exports) → IGST at the full headline rate.
Special cases: supplies to and from Special Economic Zones are zero- rated; exports are zero-rated with refund of input tax credit; supplies under Reverse Charge Mechanism (RCM) shift the GST liability from the supplier to the recipient (e.g., legal services, GTA freight).
Discount handling
Trade discounts shown on the invoice before GST reduce the taxable value. Cash discounts after GST do not—they only reduce what the customer pays. Our discount field implements the trade-discount treatment. For a ₹10,000 sale at 18% GST with a ₹1,000 trade discount:
- Taxable value = ₹10,000 − ₹1,000 = ₹9,000
- GST @ 18% = ₹1,620
- Total payable = ₹10,620
Composite vs mixed supply
When two or more supplies are bundled, GST law distinguishes:
- Composite supply — one principal supply with others naturally bundled (laptop + warranty); the principal’s rate applies to the whole.
- Mixed supply — multiple independent supplies sold for a single price (gift hamper); the highest rate among them applies to the whole.
This matters for invoices: misclassifying a mixed supply as composite can under-collect GST and create input-tax-credit mismatches at downstream filings.
HSN code ↔ rate mapping
Every taxable supply must carry an HSN (Harmonised System Nomenclature) code on the invoice. Two-digit HSN is mandatory below ₹5 crore turnover; four-digit for ₹5 crore and above; six-digit for export and SEZ supplies. The code determines the rate—always cross-check against the latest CBIC rate notification (notifications 1/2017-CT(R) through the latest GST Council meeting).
Common HSN / SAC rate quick reference
Top rates you’ll hit most often when running this GST calculator:
| Category | HSN / SAC | Rate |
|---|---|---|
| Freelance / software services (IT, design, writing) | SAC 9983 | 18% |
| Consulting / professional services | SAC 9982 | 18% |
| E-commerce commission | SAC 9985 | 18% |
| Restaurant (standalone, non-AC) | SAC 996331 | 5% (no ITC) |
| Restaurant (AC / 5-star hotel) | SAC 996331 | 18% (with ITC) |
| Textiles, apparel < ₹1,000 | HSN 6101-6117 | 5% |
| Textiles, apparel ≥ ₹1,000 | HSN 6101-6117 | 12% |
| Mobile phones + accessories | HSN 8517 | 18% |
| Laptops / computers | HSN 8471 | 18% |
| ACs, refrigerators > 1.5 ton | HSN 8415 / 8418 | 28% |
| Cars (petrol, small) | HSN 8703 | 28% + 1% cess |
| Cars (SUV, large) | HSN 8703 | 28% + 17-22% cess |
| Gold / silver jewellery | HSN 7113 | 3% |
| Milk, fresh fruit, vegetables | HSN 0401-0710 | 0% |
| Books, newspapers | HSN 4901-4902 | 0% |
When in doubt, run the HSN on CBIC’s HSN finder (cbic-gst.gov.in) or cross-check with your CA before finalising an invoice. Misclassification is the single biggest ITC-mismatch trigger at downstream filings.
Worked examples — common invoice scenarios
Five real-world scenarios the GST calculator handles daily:
1. Freelance software invoice — ₹1,50,000 to intra-state client
- Base: ₹1,50,000, rate 18% (SAC 9983), intra-state
- CGST 9% = ₹13,500
- SGST 9% = ₹13,500
- Total invoice = ₹1,77,000
- Client pays ₹1,77,000; you remit ₹13,500 each to CGST & SGST accounts
2. E-commerce sale to out-of-state buyer — ₹10,000 apparel
- Base: ₹10,000, rate 12% (₹1,000+ apparel), inter-state
- IGST 12% = ₹1,200
- Total invoice = ₹11,200
- No CGST/SGST split — full IGST goes to central pool, reallocated to buyer’s state
3. Restaurant bill with trade discount — AC restaurant
- Gross food: ₹1,000, trade discount ₹100 (10%)
- Taxable value: ₹900, rate 5% (standalone non-AC) OR 18% (AC)
- At 5%: GST = ₹45, total payable = ₹945
- At 18%: GST = ₹162, total payable = ₹1,062
- Restaurant’s AC status and whether it’s inside a 5-star hotel decides the rate
4. Reverse GST calc — extract GST from ₹59,000 software invoice
- Inclusive MRP: ₹59,000, rate 18%
- Base = ₹59,000 / 1.18 = ₹50,000
- GST = ₹59,000 − ₹50,000 = ₹9,000
- Useful for: input tax credit working, comparing pre-GST quotes, reconciling e-commerce settlement statements
5. Composition scheme trader — ₹8 lakh month turnover
- Annual turnover below ₹1.5 crore → eligible for composition scheme
- Monthly GST = 1% × ₹8,00,000 = ₹8,000
- No ITC available; cannot charge GST separately on invoices
- Compare vs regular scheme: 18% on ₹8L with full ITC claim on input purchases — usually more complex but sometimes cheaper for B2B
Common mistakes to avoid
- Mixing up forward and reverse modes. If your invoice already has GST baked in (MRP), use reverse. If the client has given you a base quote, use forward. The GST calculator clearly labels both — pick the right toggle.
- Charging CGST+SGST on inter-state supplies. If your registered state differs from the buyer’s state (“place of supply”), you must issue IGST, not CGST+SGST. Wrong application triggers notice at GSTR-1 filing and loss of ITC for the buyer.
- Ignoring compensation cess on 28% items. Cars, tobacco, aerated drinks — the headline 28% is only part of the story. The GST calculator has a cess field; always populate it for these HSNs.
- Applying GST on the gross after discount instead of the post-discount net. Trade discounts shown on the invoice reduce taxable value. The GST calculator handles this correctly when you enter discount separately — not by reducing the amount field manually.
- Using outdated HSN codes. CBIC revises HSN classifications at almost every GST Council meeting. Always verify the current rate before invoicing — a 2017-era rate may no longer be correct in FY 2026-27.
- Confusing 0% (zero-rated), nil-rated, and exempt. The customer pays no GST in all three cases, but the supplier’s ITC refund differs significantly. Exports and SEZ supplies are zero-rated (full refund); fresh produce and books are exempt/nil-rated (no refund).
- Forgetting RCM (Reverse Charge Mechanism). For some services (legal, GTA freight, rental from unregistered landlord), the buyer pays the GST to the govt directly, not the supplier. The GST calculator shows the GST number; your accounting team needs to flag it as RCM and pay separately.
Frequently asked questions
- Is GST charged on the discount or on the gross?
- On the post-discount value when the discount is shown on the invoice (Section 15 valuation rules). Discounts given separately via credit note still reduce taxable value if the recipient reverses corresponding ITC.
- Why does my invoice show CGST and SGST instead of IGST?
- Because the place of supply is in the same state as the supplier’s registered address. If you ship to a different state, the same supplier should issue an IGST invoice for that consignment.
- When is GST 0% vs nil-rated vs exempt?
- All three result in no GST being collected from the customer, but the input-tax-credit treatment differs: zero-rated (exports / SEZ) allows full ITC refund; nil-rated and exempt do not allow ITC on inputs used.
- How accurate is this calculator?
- Every result is computed with high-precision decimal arithmetic and cross-checked against CBIC published rate notifications and the ClearTax HSN finder. Sixteen real-world fixture rows and 300+ property-based assertions run on every commit.
Sources
- CBIC notifications 1/2017-CT(R) and amendments (
cbic-gst.gov.in) - GST Council meeting decisions (
gstcouncil.gov.in) - IGST Act 2017, Sections 10–13 (place of supply)
- CBIC Compensation Cess (Rate) notifications
Disclaimer. MoneyKit results are for informational purposes only and should not be construed as tax advice. HSN classification, place-of-supply determination, and input tax credit eligibility require professional judgement—consult a Chartered Accountant or GST practitioner for binding decisions.