Add GST or extract it from a total
Use a selected or custom percentage to calculate the base amount, GST amount, and tax-inclusive total. The result also shows equal CGST and SGST halves as a calculation aid. You must select the rate that applies to your supply; presets are arithmetic shortcuts, not a current tax-rate lookup.
How to use the calculator
- Select Add GST for a price before tax, or Remove GST for a tax-inclusive price.
- Enter a nonnegative amount in rupees.
- Choose a preset percentage or enter a Custom rate.
- Select Calculate GST and read the original amount, total GST, and final total.
Worked example: 18% GST
Adding 18% to Rs 1,000 gives Rs 180 GST and a total of Rs 1,180. The displayed halves are Rs 90 CGST and Rs 90 SGST. Removing 18% from Rs 1,180 recovers the same Rs 1,000 base and Rs 180 tax.
Calculation formulas
For Add GST: tax = base × rate / 100. For Remove GST: base = total / (1 + rate / 100), and tax = total minus base. Amounts are displayed to two decimal places; rounding of individual components can differ by a paisa from the total.
Scope and limitations
This page has no transaction-type selector, separate IGST result, cess input, or copy button. It does not identify tax classifications, check place of supply, determine exemptions, validate invoices, or file returns. A custom percentage performs one percentage calculation; it does not model a separate cess charge.
Common questions
Can I use a rate that is not listed?
Yes. Choose Custom and enter the percentage, including decimals where needed. Confirm the applicable rate independently before using the result on an invoice.
Why is subtracting 18% from a total different?
Tax-inclusive prices already contain the tax. Divide by 1.18 to recover a base at 18%; subtracting 18% of the total gives a different and incorrect base.
Does my amount leave the page?
The arithmetic runs in your browser without submitting the entered amount. Loading the site may still request its normal assets.
Related calculations
Use the Percentage Calculator to compare values or the Discount Calculator to work out a price reduction before calculating tax. The Invoice Generator can help format an invoice after you verify its required details.