Reverse Sales Tax Calculator
Work backward from a tax-inclusive total to find the pre-tax price and the exact tax amount for any sales tax rate.
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How to use this calculator
Divide the total (including tax) by 1 plus the decimal tax rate to extract the original pre-tax price. The tax amount is the total minus the pre-tax price.
- 1
Enter the total amount you paid, tax already included (e.g. the receipt total).
- 2
Enter the tax rate that was applied (sales tax %, VAT %, or GST %).
- 3
The calculator extracts the pre-tax price and the exact tax amount.
- 4
Use this to verify that the tax charged was correct.
Frequently asked questions
Why can't I just multiply by the tax rate to find the tax?
That would give you the tax on the pre-tax price, not on the total. For a 10% tax, if the total is $110: the pre-tax price is $110 / 1.10 = $100, and tax = $10. Multiplying $110 × 10% = $11 — which is wrong. The reverse formula correctly divides by (1 + rate).
Does this work for VAT (Value Added Tax)?
Yes. VAT is typically quoted as a percentage added to the pre-tax price — the same math applies. UK VAT is 20%, EU standard is 20–25%, India GST ranges from 0–28%, Australia GST is 10%. Enter the applicable rate and this calculator works globally.
What is "tax as % of total"?
This is the tax amount divided by the total including tax — sometimes called the "tax-inclusive rate" or "VAT fraction." For a 20% VAT: tax fraction = 20/120 = 16.67%. This matters when calculating input tax credits in VAT/GST systems.
How do I reverse multiple taxes stacked together?
Combine the tax rates algebraically. If an item has a 5% state tax and a 2% city tax applied on top of each other (cascading): effective rate = (1.05 × 1.02) − 1 = 7.1%. Enter 7.1 as the combined rate. If they are applied to the same base (non-cascading), simply add them: 7%.
How to reverse-calculate sales tax
The reverse tax formula explained
When a price includes tax, the formula to extract the pre-tax amount is: Pre-tax = Total ÷ (1 + rate). This works because the total is 100% + tax% = (1 + rate) times the pre-tax price. Dividing by (1 + rate) reverses the multiplication. A common mistake is subtracting the tax percentage directly — e.g. subtracting 10% from $110 gives $99, not the correct $100.
Sales tax vs VAT: same math, different structure
US sales tax is collected only at the final retail stage and is typically shown separately on receipts. VAT (Value Added Tax) used in over 160 countries is collected at every stage of production, with businesses reclaiming input VAT. For consumers calculating what they actually paid in tax, both systems produce the same reverse-tax calculation. The rates differ significantly: US sales tax 0–10%; European VAT 20–27%; Indian GST 0–28%.
Business use: verifying receipts and claiming VAT back
Businesses registered for VAT/GST can reclaim the tax paid on business expenses. To claim correctly, you need to accurately separate the pre-tax amount from the tax amount on each receipt. This calculator makes that split precise. For UK VAT reclaims, the tax fraction is VAT rate ÷ (100 + VAT rate): at 20% VAT, the fraction is 20/120 = 1/6.
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