Reverse Tax Calculator

You have a receipt for £120 that includes 20% VAT, but you need the original price before tax. A reverse tax calculator extracts the net amount and the tax component from any tax-inclusive total – whether the tax is VAT, GST, or sales tax.

The calculator above returns the pre-tax price and the tax amount instantly. Below is the formula it uses, worked examples, and a reference table of current rates.

How Reverse Tax Calculation Works

The reverse method starts from a gross (tax-inclusive) amount and works backwards to the net. The core formula:

Net Price = Gross Price ÷ (1 + Tax Rate)

The tax rate is expressed as a decimal: 20% becomes 0.20, 7.25% becomes 0.0725.

The tax amount is the difference:

Tax Amount = Gross Price − Net Price

You can also calculate the tax directly without finding the net first:

Tax Amount = Gross Price × [Tax Rate ÷ (1 + Tax Rate)]

Both approaches produce identical results.

Worked Example – 20% VAT

A UK invoice totals £600 including 20% VAT.

1. Convert the rate: 20% → 0.20
2. Net price: £600 ÷ 1.20 = £500.00
3. VAT amount: £600 − £500 = £100.00

Verification: £500 × 1.20 = £600 ✓

Worked Example – US Sales Tax

A purchase in California totals $53.70 with 7.25% sales tax.

1. Net price: $53.70 ÷ 1.0725 = **$50.07**
2. Tax amount: $53.70 − $50.07 = $3.63

Verification: $50.07 × 1.0725 ≈ $53.70 ✓

Common Tax Rates (2026)

* Canada’s HST combines the 5% GST with a provincial component; total rates range from 5% in GST-only provinces to 15% in Nova Scotia.

** US sales tax varies by state, county, and city; local surcharges can push the effective rate above 10% in some areas.

Tax rates change; confirm the current rate with your national tax authority before filing.

When Do You Need a Reverse Tax Calculator?

• VAT reclaims – Businesses registered for VAT can reclaim input tax on expenses, but many receipts show only the total. Reverse-calculating extracts the reclaimable tax portion.
• Bookkeeping entries – Accounting software typically requires net and tax values posted to separate accounts. If a supplier invoice lists only the gross, you must back out each component.
• Expense reporting – Employees submitting claims need to split a total into net cost and tax for correct reimbursement and tax deduction tracking.
• Price verification – Confirming that a quoted total was calculated at the correct rate, especially when discounts or multi-rate items appear on the same invoice.
• Cross-border transactions – Import VAT and GST are often assessed on the total landed cost; reverse calculation separates the customs value from the tax.

What Is the Difference Between Forward and Reverse Tax Calculation?

Forward calculation multiplies; reverse calculation divides by the same factor. They are exact inverses.

Tips for Accurate Reverse Tax Calculations

• Use the correct rate – Applying 20% when the actual rate is 19% creates a material error on large invoices. Check the rate for the relevant jurisdiction and date.
• Handle mixed-rate receipts separately – A single receipt may include standard-rate and reduced-rate items. Calculate each group at its own rate, then sum the net amounts.
• Round at the final step – Carry full precision through the calculation and round only the final net and tax figures to two decimal places. Intermediate rounding introduces drift.
• Watch for tax-exempt items – Some products (books, children’s clothing, basic groceries) are zero-rated or exempt in certain jurisdictions. Strip these from the total before applying the reverse formula.

For official VAT and sales tax rates, refer to HMRC (UK) or the OECD Tax Database (international overview).