GST Calculator — Reverse, Multi-item, All Slabs & Net Payable
✓ Verified against CGST Act Section 9 methodologyUpdated 23 July 2026All 4 slabs + CGST/SGST/IGST split
Calculate GST four different ways — add it to a base amount, extract it from an inclusive total, split it as CGST + SGST or IGST, or work out the net GST payable after input tax credit. Plus a multi-item invoice mode, a composition scheme calculator, and the bill-checking maths every consumer and small business should know.
The 18% on your bill isn't what the government actually gets
Every time you see "GST 18%" on a restaurant bill or a service invoice, there is a common misunderstanding: that this number is what the government collects and pockets from your specific purchase. That is not how GST works, and understanding this changes how you read every bill going forward.
GST is a tax on value added, not on the final purchase. The seller collects 18% from you, yes — but the seller has already paid GST on their own purchases (rent, ingredients, packaging, electricity, wages if any). They subtract what they paid (called input tax credit) from what they collected, and remit only the difference to the government. On a ₹100 dish where the restaurant paid ₹40 of GST-covered inputs at 18%, the actual GST that leaves the restaurant's account and reaches the government from your bill is ₹18 − ₹7.20 = ₹10.80 — not ₹18.
Second thing worth knowing: the 18% you see on the bill is not one tax. On an intrastate bill (buyer and seller in the same state), it is split into 9% CGST going to the Centre and 9% SGST going to the state. On an interstate bill, the entire 18% is IGST — collected by the Centre and later shared with the destination state. Small stores frequently print "GST 18%" without disclosing this split — a technically non-compliant invoice.
Third thing: the four slabs — 5%, 12%, 18%, 28% — are not evenly applied. Most goods and services sit at 18%. Restaurants (non-AC and standalone) are at 5% but cannot claim input credit. Luxury items and sin goods at 28% may carry additional compensation cess. Composition-scheme businesses (turnover under ₹1.5 crore) pay a flat 1% / 5% / 6% depending on category and do not charge GST separately — so a ₹500 bill from your neighbourhood tailor may have zero visible GST but the tailor still pays 6% to the government on their entire turnover.
What this page does differently: the calculator below has four modes — Standard (add GST), Reverse (extract from total), Compare-all-slabs, and Net Payable (output minus input credit). Under the calculator is a multi-item invoice builder, a composition-scheme calculator, and a section on the mistakes worth spotting on the bills you actually receive. Read them the next time a restaurant hands you a slip and it will make more sense than it ever has.
₹10,000
18%
₹11,800
18%
₹10,000
Enter total output GST collected (from sales invoices) and total input GST paid (from purchase invoices). Net GST payable to the government is the difference.
₹18,000
₹7,200
GST amount
₹1,800
Base amount
₹10,000
Total (inc. GST)
₹11,800
Rate applied
18%
Effective on total
15.25%
CGST (9%)
₹900
SGST (9%)
₹900
IGST
—
0% NIL
₹0
GST: ₹0
Total: ₹10,000
3% GOLD
₹300
GST added
Total: ₹10,300
5% ESSENTIAL
₹500
GST added
Total: ₹10,500
12% STANDARD
₹1,200
GST added
Total: ₹11,200
18% GENERAL
₹1,800
GST added
Total: ₹11,800
28% LUXURY
₹2,800
GST added
Total: ₹12,800
Multi-item invoice — build a real GST invoice
Add line items with different GST rates and see the per-slab breakdown at the bottom. This is how a real invoice looks when you have items at multiple rates (very common for restaurants, retail stores, and mixed-service businesses).
Item
Amount
GST
Composition scheme calculator — for small businesses
If your annual turnover is under ₹1.5 crore (₹75 lakh in special-category states), you can opt into the composition scheme. Instead of charging 5-28% GST to customers and reclaiming input credit, you pay a flat percentage on your turnover to the government. Simpler paperwork, but you cannot charge GST from customers and you cannot claim input credit.
₹5,00,000
Quarterly GST to pay government
₹30,000
Annualised GST
₹1,20,000
Effective on turnover
6.0%
Rule
Section 10 CGST Act
Cannot claim ITC
Yes — trade-off
When it's worth it: if your input purchases are small (like most consulting services, tailors, or small retailers dealing mostly with unregistered suppliers), composition saves the input-credit reconciliation work and is cheaper. If input purchases are large (like manufacturing or restaurants with GST-registered ingredient suppliers), staying in the regular scheme lets you claim credit and pay net less GST — usually the better call.
GST rates by category — what falls in each slab
The GST Council meets a few times each year and can move items between slabs. This is the picture as of July 2026, sourced from the CBIC rate finder. For any specific product, verify the exact HSN code from cbic.gov.in.
Special rates: Gold and jewellery are at 3% (not in any regular slab). Rough diamonds are at 0.25%. Sin goods (tobacco, aerated drinks) attract compensation cess over and above 28% — cigarettes for example can effectively reach 60-80% of the base price. Petrol, diesel and alcohol for human consumption are outside GST entirely — they are taxed under the older VAT and excise regimes.
Three worked examples — GST as it actually appears
Example 1 · Restaurant bill (non-AC standalone) — what you actually pay
Menu total for food ordered : ₹1,000
CGST @ 2.5% (on food only) : ₹25
SGST @ 2.5% (on food only) : ₹25
Sub-total after GST : ₹1,050
Service charge (optional) : ₹50 ← you can decline this; CCPA July 2022
─────
Grand total : ₹1,100
Notes:
- Standalone non-AC restaurants charge 5% GST (2.5% CGST + 2.5% SGST)
- GST is charged on food value ONLY, not on service charge
(see the Mistake 1 section below — a common overcharge)
- Restaurants in five-star hotels charge 18% instead
- Restaurants cannot claim input tax credit at the 5% rate — a trade-off
- If you accept service charge, it goes to staff, not the government
- CCPA (July 2022): you can ask for service charge to be removed
Example 2 · Freelance service invoice — interstate (Bangalore to Delhi)
Consulting fee : ₹50,000
IGST @ 18% : ₹9,000
──────
Total invoice value : ₹59,000
Notes:
- Interstate transaction — full 18% is IGST, not split into CGST/SGST
- Delhi client (GST-registered) can claim ₹9,000 as input tax credit
- Client's net GST cost from this invoice: ₹0, because they set it off
against their output GST liability
- If freelancer is under ₹20L annual turnover, no GST is chargeable
and this becomes a simple ₹50,000 invoice — but declare "unregistered
supplier" on the invoice
Example 3 · Retailer's monthly GST return — the real payable
SALES (output GST collected)
- Sold goods worth : ₹5,00,000
- Output GST @ 18% : ₹90,000
PURCHASES (input GST paid)
- Bought goods worth : ₹3,00,000 → GST paid ₹54,000
- Rent (18%) : ₹40,000 → GST paid ₹7,200
- Electricity, phone, misc : ₹10,000 → GST paid ₹1,800
- Total input GST paid : ₹63,000
NET GST PAYABLE = ₹90,000 − ₹63,000 = ₹27,000
That's what goes to the government. Note: input credit only works
if the supplier has filed their GSTR-1 and the invoice appears in
your GSTR-2B. Missing supplier compliance = credit blocked =
you pay the full ₹90,000.
Input tax credit — the concept that makes GST different
The entire logic of GST rests on Input Tax Credit (ITC). It is what prevents the "tax on tax" cascade that the old VAT + excise regime had. If you understand ITC, you understand GST.
How it works, in one line
Every registered business collects GST on what it sells (output GST) and pays GST on what it buys (input GST). The business remits only the difference to the government — output minus input. If output is greater, you pay the balance. If input is greater (common for exporters and manufacturers), the government owes you a refund.
Five things that block ITC (and cost businesses lakhs every year)
Supplier hasn't filed GSTR-1. If the vendor didn't upload the invoice to the GST portal, it won't appear in your GSTR-2B, and you can't claim credit. Chase vendors monthly.
Invoice not paid within 180 days. ITC claimed on unpaid invoices must be reversed after 180 days from invoice date, with interest.
Personal use expenses. ITC on things used personally (not business-related) is not admissible — food, entertainment, membership fees.
Certain blocked items. Rule 42 blocks ITC on motor vehicles under 13 seats (except when used for driving school, transport of goods, further supply), on food and outdoor catering (with narrow exceptions), on works contract services for immovable property (except by construction contractors themselves).
Exempt outward supplies. If part of your business is GST-exempt (like agricultural produce), you can only claim proportional ITC on inputs used for taxable supplies. The apportionment ratio is a common audit finding.
Practical tip: reconcile GSTR-2B with your purchase register every month, not every quarter. Chasing a vendor for a missing invoice at month-end while it's fresh is easier than chasing them six months later during an audit.
Common mistakes on the bills you receive
Once you know GST maths, you can spot errors on the bills you get. Some are outright incorrect; some are technically wrong but hard to challenge. Either way, worth knowing.
Mistake 1: GST charged on service charge
Correct approach: GST is charged only on the food value, not on service charge (which is a hotel-added fee, not part of the taxable value under GST). A bill showing "food ₹1000 + service charge ₹100 = ₹1100, GST @ 5% = ₹55" is wrong — GST should be ₹50 on the ₹1000 food value. This is a common overcharge in mid-tier restaurants.
Mistake 2: GST charged before discount
Correct approach: if the discount is on the invoice itself, GST is charged on the post-discount amount. A ₹1000 item sold at ₹800 with GST at 18% should show GST as ₹144 (18% of ₹800), not ₹180 (18% of ₹1000).
Mistake 3: No CGST/SGST/IGST split on an intrastate invoice
Correct approach: for a valid tax invoice on intrastate supply, CGST and SGST must be shown separately. A single "GST @ 18%" line without split makes the invoice non-compliant. If you're claiming input credit, this may be challenged.
Mistake 4: GSTIN missing or incorrect
Correct approach: any tax invoice from a registered business must show a valid 15-character GSTIN. Verify GSTINs at services.gst.gov.in/services/searchtp. Fake or wrong GSTINs invalidate the invoice for input credit purposes and, if intentional, are a criminal offence under Section 132.
Mistake 5: Reverse charge not disclosed
If you receive services from an unregistered supplier (goods transport agent, legal services, director's remuneration), you should be paying GST under reverse charge. Many businesses forget this line entirely. A GST audit catches it in year 3, with interest.
GST formulas — the maths in every mode
STANDARD (add GST):
GST amount = Base × Rate / 100
Total = Base + GST amount
= Base × (1 + Rate / 100)
REVERSE (extract GST from an inclusive total):
Base = Total × 100 / (100 + Rate)
GST amount = Total × Rate / (100 + Rate)
CGST/SGST split (intrastate):
CGST = GST amount / 2
SGST = GST amount / 2
IGST (interstate):
IGST = GST amount (single tax, no split)
NET GST PAYABLE:
Net payable = Output GST − Input GST credit
Why the reverse formula divides by (100 + Rate)
When a total already includes GST, the total represents 100% base + rate% GST = (100 + rate) parts. To recover the base, take Total × 100 / (100 + rate). To recover the GST, take Total × rate / (100 + rate). Common mistake: dividing the total by (1 + rate/100) works, but subtracting rate% from the total does not — that will underestimate GST because the rate is applied to a smaller base.
As of July 2026, GST has four main rates: 5% (essentials — packaged food, transport, basic apparel), 12% (processed food, computers, some services), 18% (most services, restaurants, telecom, financial products), and 28% (luxury goods, sin items — with additional compensation cess on tobacco and aerated drinks). There's also 0% (nil-rated — fresh food, milk, books) and special rates of 3% for gold and 0.25% for rough diamonds. Any of these can change through GST Council decisions — verify from cbic.gov.in for current classification of a specific product.
Is service charge on a restaurant bill GST? ▼
No. Service charge and GST are two separate things. GST is a mandatory government tax at 5% (for most restaurants) or 18% (for AC restaurants in five-star hotels). Service charge is a discretionary hotel-added fee, typically 5-10%, that goes to the restaurant, not the government. CCPA guidelines from July 2022 say service charge cannot be added without explicit customer consent — you can ask for it to be removed. GST is then charged on the food value only, not on service charge.
What is the difference between CGST, SGST and IGST? ▼
On an intrastate transaction (buyer and seller in the same state), the GST is split equally between Central GST (CGST, to the Centre) and State GST (SGST, to the state). An 18% intrastate GST is 9% CGST + 9% SGST. On an interstate transaction, the entire tax is charged as Integrated GST (IGST) which the Centre collects and later apportions to the destination state. IGST at 18% is 18% IGST, not 9+9. On invoices, all three must be disclosed separately.
What is input tax credit and how does it work? ▼
Input Tax Credit (ITC) is the GST you paid on business purchases that you can deduct from the GST you collect on business sales. If you sold ₹1,00,000 worth of goods at 18% GST (collected ₹18,000), and bought ₹40,000 of inputs at 18% GST (paid ₹7,200), your net GST payable is ₹18,000 − ₹7,200 = ₹10,800. ITC is only available if your supplier has actually filed their GSTR-1 and the invoice appears in your GSTR-2B. Missing supplier compliance kills the credit.
Who needs to register for GST? ▼
Registration is mandatory if your annual turnover exceeds ₹40 lakh for goods (₹20 lakh in special-category states) or ₹20 lakh for services (₹10 lakh in special-category states). It is also mandatory regardless of turnover if you make interstate supplies of goods, sell through e-commerce platforms like Amazon or Flipkart, are liable under reverse charge, or are a non-resident taxable person. Voluntary registration below the threshold is allowed and often useful — it lets you claim input credit and gives client-facing credibility.
Do I need GSTIN as a freelancer? ▼
Only if your annual freelance revenue exceeds ₹20 lakh (₹10 lakh in Northeastern and hilly states). Below that, no registration needed and no GST to charge — but you should still disclose services on invoices as "unregistered supplier". If your clients are companies that want to claim input credit, they will prefer you registered. Cross-border services (any client outside India) are treated as exports and, if registered, are zero-rated with refund of input credit. Many freelancers register voluntarily just to make the export refund work.
What is the reverse charge mechanism? ▼
Under reverse charge, the recipient of goods or services pays the GST directly to the government instead of the supplier collecting and remitting it. This applies in specific cases: services from unregistered suppliers (turnover below threshold), services from goods transport agencies, legal services from advocates, and services from directors to their companies. The reverse charge amount is not part of your total input credit until you actually deposit it. RCM is a common source of GST audit findings — most businesses forget to track it.
What is the GST composition scheme? ▼
A simplified scheme for businesses with turnover under ₹1.5 crore (₹75 lakh in special-category states). Instead of paying GST at 5/12/18/28% and claiming input credit, you pay a flat percentage on turnover: 1% for traders and manufacturers, 5% for restaurants, and 6% for service providers (up to ₹50 lakh turnover). You cannot charge GST from customers, cannot claim input tax credit, and cannot make interstate outward supplies. The tradeoff — simplicity and lower rate versus loss of ITC and market limitations.
How is GST calculated on discounted items? ▼
GST is charged on the post-discount price if the discount is offered at the time of supply and shown on the invoice. If a T-shirt priced at ₹1,000 is sold at ₹800 (₹200 discount on the invoice), GST is charged on ₹800. However, if a cashback or discount comes later (after invoice), GST already paid on the full ₹1,000 does not get reduced. Trade discounts, quantity discounts, and cash discounts on the invoice all reduce the taxable value. Post-supply discounts do not, unless linked to specific supply and disclosed in advance.
What is e-invoicing and does it apply to me? ▼
E-invoicing requires you to upload every B2B invoice to the government's Invoice Registration Portal (IRP) which issues a QR code and IRN (Invoice Reference Number). As of July 2026, e-invoicing applies to all businesses with aggregate turnover above ₹5 crore in any preceding financial year since GST rollout. B2C invoices are exempt. E-invoicing is mandatory before the invoice is issued to the customer — a non-e-invoice for a covered business is not a valid tax invoice and the recipient cannot claim ITC on it.
Do I have to pay GST on rent? ▼
For residential rent — no GST if the tenant is an individual using it for their own residence. Yes 18% GST if the tenant is a company or the property is used for commercial purposes (like a co-living operator subletting). For commercial rent — 18% GST always applies if the landlord is registered under GST (or their rental income crosses ₹20 lakh in a year). The tenant, if GST-registered, can claim ITC on commercial rent. From July 2022, GST also applies when residential property is rented to a GST-registered person, under reverse charge.
Are exports zero-rated or GST-exempt? ▼
Zero-rated, not exempt — an important legal distinction. Zero-rated means the export supply is taxable at 0%, but you can claim refund of input tax credit on inputs used. Exempt means no GST is chargeable but you also cannot claim ITC. Under zero-rating, exporters have two options: pay IGST on export and claim refund, or export under Letter of Undertaking (LUT) without paying IGST. Services provided to clients outside India, paid in convertible foreign currency, qualify as export of services and enjoy the same zero-rating.
What happens if I miss a GST filing deadline? ▼
Late fee is ₹50 per day (₹25 CGST + ₹25 SGST) for regular GSTR-3B, capped at ₹5,000. For nil returns (no transactions), the fee is ₹20 per day capped at ₹500. Interest at 18% per annum applies on unpaid tax from the due date until payment. Delayed filing beyond a threshold blocks e-way bill generation for outward supplies (Rule 138E), which effectively halts your business until the return is filed. Repeat non-filers can have their GSTIN cancelled by the officer.
Is GST charged on the invoice discount or before it? ▼
Read the invoice carefully. Most Indian invoices display three lines: gross, discount, taxable value — then GST is added on the taxable value (i.e. after discount). A minority of poorly-designed invoices show GST on the gross and then subtract discount, which is technically legal only if the discount is post-supply. If you see GST calculated on a pre-discount figure and the discount is a same-invoice reduction, the calculation is wrong — you are being overcharged.
How do I calculate GST from a total that includes it? ▼
Use reverse-GST maths. If the total (inclusive of GST) is T and the rate is r%, then base = T × 100 / (100 + r), and GST amount = T × r / (100 + r). Example: a bill total of ₹11,800 at 18% GST — base = 11,800 × 100 / 118 = ₹10,000, GST = 11,800 × 18 / 118 = ₹1,800. The reverse-GST tab in the calculator above does this. Common consumer trap: adding r% to the total by mistake instead of extracting r% from within it.
Important: All calculations follow the GST arithmetic prescribed by the CGST Act and are correct for the inputs provided. GST rates change through GST Council notifications — the rates and thresholds cited here were verified against CBIC and GST portal announcements as of 23 July 2026. HSN-code-specific classifications and exemptions can differ from the general categories shown; consult a Chartered Accountant, a GST practitioner, or the CBIC rate finder for treatment of specific products or services. This page is educational and does not constitute tax or legal advice. Errors in GST classification can trigger penalties and interest under Section 122 of the CGST Act — take professional help for anything ambiguous.