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GST/VAT Calculator
GST / VAT Calculator adds a tax rate to an amount or strips it back out, returning the net amount, the tax component and the gross total, so an invoice figure can be checked in either direction.
How to use GST/VAT Calculator
- Choose whether you want to add tax to a net amount or extract tax from a gross one.
- Enter the amount and the tax rate.
- Calculate to see the net, tax and gross values together.
Where GST/VAT Calculator is useful
- Checking the tax line on an invoice you received.
- Working out the price to quote before tax.
- Splitting a gross expense into its net and tax parts for bookkeeping.
Formats, algorithms and limits
Adding tax multiplies the net amount by one plus the rate. Removing tax is the exact inverse — the gross is divided by one plus the rate, which is why a 20% VAT on 120 comes back as 100 net rather than 96. The three figures are always shown together so you can see which direction was applied.
Troubleshooting and honest limits
- Never simply subtract the tax percentage from a gross figure: dividing by one plus the rate is the correct reversal.
- Check the direction before entering the number; the add and remove modes are deliberately separate.
- Some countries use reduced rates for certain goods, so confirm the applicable rate before invoicing.
Frequently asked questions
What is the difference between the add and remove modes?
Add mode treats your figure as net and adds the tax on top. Remove mode treats it as gross and extracts the tax that is already inside it.
Why is extracting 18% from 118 not 100 minus 18%?
Because the tax was charged on the net figure, so the gross is 118% of it. Dividing by 1.18 returns the original 100 exactly, which the tool does for you.
Can it calculate for any country?
The arithmetic is universal; the rate is yours to enter. Look up the applicable rate for your jurisdiction and product category.
Does it round like an accountant would?
Values are shown to two decimal places, which matches normal currency rounding for the amounts used in everyday invoices.
Related tools
Page written and reviewed by the FreeConvertio engineering team on 2026-10-14. GST/VAT Calculator runs entirely in your browser — no uploads, no account and no daily limits.