How to Calculate Sales Tax, VAT and GST
Sales tax, VAT, and GST go by different names around the world, but the maths is the same: a percentage added to the price of goods and services. Whether you're pricing a product, checking a receipt, or invoicing a client, knowing how to add (and remove) tax is a genuinely useful everyday skill.
The three names, one idea
Sales tax (US) is added at the final point of sale. VAT (Value Added Tax, used across the UK, EU and many countries) and GST (Goods and Services Tax, used in Australia, India, Canada and others) are collected at each stage of production but ultimately paid by the consumer. For everyday calculations, you treat all three the same way: a percentage on top of the price.
Adding tax to a price
Multiply the price by the tax rate (as a decimal) and add it on. For a $200 item at 8% sales tax:
Tax = 200 × 0.08 = $16
Total = 200 + 16 = $216
The one-step shortcut: multiply by 1 plus the rate. 200 × 1.08 = $216 in a single move.
Working backwards from a total
This is the part that trips people up. If a price includes 20% VAT and you want the pre-tax amount, you do not just take 20% off — you divide by 1.20:
£120 inclusive ÷ 1.20 = £100 before VAT (so £20 is the VAT)
Dividing, not subtracting, is the key. Taking 20% off £120 would wrongly give £96.
Why the difference matters for business
If you're VAT or GST registered, you charge tax on sales and reclaim it on purchases, so getting the inclusive/exclusive maths right keeps your books and invoices correct. Always state clearly whether a quoted price includes or excludes tax — ambiguity here causes disputes.
Calculate any of them instantly
Our calculators handle all three: the sales tax calculator, the VAT calculator (which also works backwards from an inclusive total), and the GST calculator. Pair them with the discount calculator to find the true price after a sale.
Bottom line
Adding tax means multiplying by 1 plus the rate; removing it means dividing by that same figure. Sales tax, VAT, and GST differ in how they're collected but not in this everyday arithmetic. Get the direction right — multiply to add, divide to remove — and you'll never miscalculate a total again.
