Quick answer
To calculate GST, multiply the base amount by the applicable rate (5%, 12%, 18%, or 28%) and add it to the price. This free calculator does it instantly and also works in reverse to remove GST from a tax-inclusive total. Everything you type stays in your browser.
Last updated: July 2026 · Free · Runs entirely in your browser
How to use the GST calculator
Enter your amount, choose the GST rate (5%, 12%, 18%, or 28%), and pick whether the amount is exclusive of GST (you want to add GST) or inclusive (you want to remove GST). The calculator instantly shows the base amount, the GST, and the total, and splits the tax into CGST and SGST for a within-state sale or shows IGST for an inter-state sale.
Forward GST vs reverse GST
Forward (add GST): you have the base price and want the final price. Reverse (remove GST): you have the final, GST-inclusive price and want the base price plus the tax hidden inside it. Reverse GST is where most people slip up, because you cannot simply subtract the percentage. The formula is base = amount / (1 + rate/100), and GST = amount - base. This tool does that back-calculation for you.
GST rates in India, at a glance
The standard slabs are 0%, 5%, 12%, 18%, and 28%. 18% is the most common rate for services and software. For a sale within the same state the rate is split into CGST and SGST (half each); for an inter-state sale the whole rate is charged as IGST.
Who it is for
- Freelancers and small businesses raising a GST invoice.
- Shop owners pricing goods with tax included or excluded.
- Anyone checking whether a bill has the GST calculated correctly.
Need to get paid after quoting a price? Create a UPI payment link in seconds, or read the deeper guide on how to add and remove GST in India. Browse all free tools.
Why this GST calculator
It is free, needs no signup, and runs entirely in your browser, so nothing you type is uploaded to a server. It works on your phone and your laptop, and handles both GST-inclusive and GST-exclusive amounts with the CGST, SGST, and IGST split.
Frequently asked questions
- How do I calculate reverse GST?
- Divide the GST-inclusive amount by (1 + rate/100) to get the base amount, then subtract the base from the total to get the GST. At 18%, a total of 118 gives a base of 100 and GST of 18. This calculator does it automatically when you choose the inclusive option.
- What is the difference between CGST, SGST, and IGST?
- For a sale within the same state, GST is split equally into CGST (central) and SGST (state). For a sale between two states, the full rate is charged once as IGST (integrated). The total tax is the same either way.
- Which GST rate applies to software and SaaS?
- Software and SaaS in India are generally taxed at 18% under GST.
- Is this GST calculator free?
- Yes. It is completely free, needs no account, and runs in your browser with no data uploaded.
- Can it handle both GST-inclusive and GST-exclusive amounts?
- Yes. Choose add GST for an exclusive base price, or remove GST for a final inclusive price, and the tool computes the rest.
Executive Architecture Summary
The BeginThings GST Calculator implements standardized forward (tax-exclusive) and reverse (tax-inclusive) mathematical algorithms for the four primary Indian Goods & Services Tax slabs: 5%, 12%, 18%, and 28%. Designed for business founders, accounting teams, and solo professionals, the engine computes exact tax splits between Central GST (CGST), State GST (SGST), and Integrated GST (IGST) in real-time within your browser's local sandbox, guaranteeing zero telemetric exposure of your commercial revenue data.
Mathematical Formulations for Forward vs. Reverse GST Calculations
Accurate commercial billing requires understanding the difference between forward tax addition and reverse tax extraction:
1. Forward GST Calculation (Tax-Exclusive Pricing)
Used when you have agreed upon a net fee or cost of goods, and tax must be added on top of the base amount:
GST Amount = Base Amount × (Tax Rate / 100)Total Invoice Amount = Base Amount + GST Amount- Example: For a software consulting retainer of ₹50,000 at 18% GST:
GST = ₹50,000 × 0.18 = ₹9,000. Total payable = ₹59,000.
2. Reverse GST Extraction (Tax-Inclusive Pricing)
Used when a client pays a flat lump sum (e.g., ₹100,000 all-inclusive), or an e-commerce retail price includes tax, and you must extract the true net revenue and tax liability for government remittance:
Base Amount = Gross Total / (1 + (Tax Rate / 100))GST Component = Gross Total - Base Amount- Example: For a lump sum payment of ₹118,000 at 18% GST:
Base = ₹118,000 / 1.18 = ₹100,000.
GST Component = ₹118,000 - ₹100,000 = ₹18,000.
Rounding Standards Under Section 170 of the CGST Act
A common error in automated accounting is incorrect fractional rounding. Under Section 170 of the CGST Act, 2017, the amount of tax, interest, penalty, fine, or any other sum payable, and the amount of refund or any other sum due, must be rounded off to the nearest rupee. Fractions of a rupee equal to or greater than 50 paise must be rounded up to one rupee, and fractions less than 50 paise are disregarded. BeginThings applies these statutory rounding algorithms automatically.
Indian GST Slab Distribution & Industry Classifications
The GST Council classifies goods and services into specific rate schedules based on economic essentiality:
| Slab Rate |
Representative Economic Sectors |
Key SAC / HSN Classifications |
Input Tax Credit (ITC) Rules |
| 0% (Nil Rated) |
Basic agricultural food staples, healthcare, education |
HSN 0101-0810, SAC 9992, 9993 |
No ITC claimable on exempt supplies |
| 5% (Low Rate) |
Passenger transport (cab aggregators), economy air travel, spices |
SAC 9964, HSN 0901-0910 |
Limited ITC (No ITC for 5% passenger transport) |
| 12% (Concessional) |
Business class air travel, construction materials, processed goods |
SAC 9964, HSN 8414 |
Full ITC available for registered businesses |
| 18% (Standard Rate) |
IT services, SaaS, marketing consulting, design, telecom |
SAC 998314 (IT), SAC 998391 (Design) |
Full ITC available across business expenses |
| 28% (Luxury & Sin) |
Luxury automobiles, consumer electronics, specialized entertainment |
HSN 8703, HSN 8415 |
Restricted ITC on personal motor vehicles |
Place of Supply (POS): Deciding CGST/SGST vs. IGST
Determining whether to split tax or levy an integrated single tax depends strictly on the Place of Supply (POS) rules under the Integrated Goods and Services Tax (IGST) Act, 2017:
- Intra-State Supply (Same State): Occurs when the supplier's registered location and the place of supply (recipient's registered address) are within the same state. Tax is equally divided: 50% to the Central Government (CGST) and 50% to the State Government (SGST). For an 18% slab, this reflects 9% CGST and 9% SGST.
- Inter-State Supply (Different States): Occurs when the supplier and recipient are in different states or Union Territories. The full 18% is collected as Integrated GST (IGST) and administered centrally before interstate revenue sharing.
Four Practical Business Calculations
- Retainer Negotiation Dissection: If a client offers a "fixed budget of ₹75,000 including all taxes", you can reverse calculate at 18% to find your true pre-tax fee (
₹75,000 / 1.18 = ₹63,559.32) and realize that ₹11,440.68 must be paid to the government.
- Input Tax Credit (ITC) Margin Defense: Calculating tax paid on laptop purchases or cloud server subscriptions (ITC eligible) to offset against output tax collected on client billing, preventing cash flow drain.
- E-Commerce Pricing Calibration: Determining catalog listing prices that maintain gross margin after absorbing 18% marketplace commissions and GST.
- Cross-Border Export Exemption: Verifying zero-rate treatment under Letter of Undertaking (LUT) to avoid erroneously charging foreign clients 18% GST.
Frequently Asked Questions
How do I calculate reverse GST from a total payment amount?
Divide the total GST-inclusive amount by (1 + Tax Rate / 100) to find the net base amount. Then subtract the base amount from the total amount to find the exact GST component. For example, with an inclusive total of ₹11,800 at an 18% rate: ₹11,800 / 1.18 = ₹10,000 base amount, and ₹1,800 GST.
What is the difference between CGST, SGST, and IGST?
CGST (Central GST) and SGST (State GST) apply when goods or services are sold within the same state (intra-state), splitting the total tax 50/50 between central and state authorities. IGST (Integrated GST) applies when the transaction crosses state borders (inter-state), and is collected by the central government.
Which GST rate applies to freelance software developers and designers in India?
The standard rate for information technology software services (SAC 998314) and graphic/creative design services (SAC 998391) is 18%. If billing domestic clients, this is levied as 9% CGST + 9% SGST (within state) or 18% IGST (inter-state).
Do I have to charge GST if my annual turnover is under ₹20 Lakhs?
No. Service providers with an aggregate annual turnover below ₹20 Lakhs (or ₹10 Lakhs in Special Category States) are exempt from mandatory GST registration. Unless you voluntarily register for GST to claim Input Tax Credit, you cannot collect GST from clients.
Is my financial data uploaded or saved when using this GST calculator?
No. All calculations are executed locally in your browser's JavaScript engine. No numbers, prices, or business financial details are transmitted to any server or recorded in any database.
