What is the formula for reverse sales tax?

If T is the total including tax and r is the tax rate as a decimal, then pre-tax price = T ÷ (1 + r) and tax amount = T − pre-tax price. For multiple tax rates, use r = r1 + r2 + … (as decimals) if they are applied on the same base.

Can I use this calculator for VAT, GST, or other taxes?

Yes. The reverse sales tax calculator works for any percentage-based consumption tax such as VAT, GST, HST, QST, or service tax. Just enter the correct combined tax rate for your region.

What if I only know the tax amount, not the rate?

If you know the total including tax and the tax amount, you can find the pre-tax price by subtracting: pre-tax price = total − tax amount. The effective tax rate is then tax ÷ pre-tax price.

Is reverse sales tax the same as removing tax from a price?

Yes. Reverse sales tax, back-out tax, and removing tax from a price all refer to the same process: starting from a tax-inclusive total and calculating the original price before tax and the tax portion.

Reverse Sales Tax Calculator

Q: How do you calculate reverse sales tax from a total?

To calculate reverse sales tax from a total including tax, divide the total by 1 plus the tax rate as a decimal. For example, with a 7% tax rate, pre-tax price = total ÷ 1.07. The tax amount is then total − pre-tax price.

Back out sales tax from a total price to find the original pre-tax amount and tax portion. Works for sales tax, VAT, GST, and more.

Mode 1: Enter total including tax and rate(s) to get base and tax. Mode 2: Enter base and tax amount to get effective rate.

Total including tax

Currency symbol

Main tax rate (%)

e.g. state or federal tax

Secondary tax (%)

e.g. local or city tax

Other tax (%)

e.g. special levy

Round to 2 decimal places

Show line-by-line breakdown

Results

Pre-tax price

–

Tax amount

–

Total including tax

–

Effective tax rate

–

Line-by-line breakdown:

Component	Amount

How to calculate reverse sales tax

Reverse sales tax means starting from a total price that already includes tax and working backwards to find:

the original price before tax (pre-tax price), and
the tax amount included in the total.

Reverse sales tax formula

Given:

$ T $ = total price including tax
$ r $ = tax rate as a decimal (e.g. 7% → 0.07)

Formulas:

Pre-tax price: \[ \text{Base} = \frac{T}{1 + r} \]

Tax amount: \[ \text{Tax} = T - \text{Base} \]

Effective tax rate (from base): \[ r = \frac{\text{Tax}}{\text{Base}} \]

Example: Backing out 7% sales tax

Suppose your receipt shows a total of $107.00 and you know the sales tax rate is 7%.

Convert 7% to decimal: $ r = 0.07 $.
Compute base price: $ \text{Base} = 107 ÷ 1.07 = 100.00 $.
Compute tax: $ \text{Tax} = 107.00 − 100.00 = 7.00 $.

So the original price before tax was $100.00 and the sales tax included in the total is $7.00.

Multiple tax rates (state + local + other)

In many places, the total tax is made up of several components (for example, state tax, county tax, and city tax). If they are all applied to the same base price, you can add the rates together:

Combined rate: \[ r_{\text{total}} = r_1 + r_2 + r_3 + \dots \]

Then use $ r_{\text{total}} $ in the reverse tax formula: \[ \text{Base} = \frac{T}{1 + r_{\text{total}}} \]

The calculator lets you enter up to three separate rates and shows both the combined rate and the tax amount attributable to each component.

Common uses for a reverse sales tax calculator

Checking how much tax you actually paid on a receipt.
Preparing bookkeeping entries that require net (pre-tax) amounts.
Converting tax-inclusive prices to tax-exclusive prices for invoices or quotes.
Estimating sales tax liability when you only know gross revenue.
Comparing prices across regions with different tax systems (sales tax vs VAT/GST).

Tips and caveats

Always use the combined tax rate for your location (state + local + special taxes).
Receipts may round each line item, so your manual calculation can differ by a cent.
This tool assumes a single percentage-based tax applied to the base price.
It does not handle tax on tax or tiered tax brackets.

FAQ: Reverse sales tax

How do you calculate reverse sales tax from a total?

Divide the total including tax by 1 plus the tax rate as a decimal. For example, with a 7.5% tax rate:

\[ \text{Base} = \frac{T}{1 + 0.075} \] \[ \text{Tax} = T - \text{Base} \]

Can I use this for VAT, GST, or HST?

Yes. VAT, GST, HST, QST and similar consumption taxes are all percentage-based. As long as you know the combined rate, the same reverse tax formula applies.

What if I know the tax amount but not the rate?

Use the “Base + tax amount” mode. Enter the base price and the tax amount. The calculator will compute:

Total including tax (base + tax)
Effective tax rate = tax ÷ base × 100%

Why is my result off by a cent compared to the receipt?

Many point-of-sale systems round tax on each line item, then sum the rounded values. The reverse tax formula works on the total, so small rounding differences of 1–2 cents are normal and not an error.

Does this handle tax-exempt items or discounts?

This calculator assumes the entire amount is taxable at a single rate. If your receipt includes tax-exempt items or discounts, you should first isolate the taxable portion or work line by line using the same formula.