tax calculator

Sales Tax Calculator

The Sales Tax Calculator models the arithmetic relationship between a before-tax price, an entered sales tax rate, the tax amount, and the after-tax price. It can add tax, remove tax from a tax-inclusive total, or estimate an effective entered rate from before-tax and after-tax prices.

Result

Result summary: Sales tax is $6.50 on a $100.00 purchase, making the after-tax price $106.50.
Before tax price: $100.00
Sales tax rate: 6.50%
Sales tax amount: $6.50
After tax price: $106.50

Scenario nameNotes

Save this result, then use saved scenarios to switch between assumptions.

How the Sales Tax Calculator works

Use this calculator when you already have a rate assumption and want to check checkout arithmetic, read a receipt, or compare a tax-exclusive price with a tax-inclusive total. Use Discount before Sales Tax when a markdown changes the taxable starting price, VAT when the question is a VAT-style net or gross price, Payment or Loan Payment when the tax-inclusive amount feeds a financing estimate, and official state, local, or tax authority tools when you need a current rate or rule.

For after-tax price, convert the entered rate to a decimal with r = sales tax rate / 100, calculate tax amount = before-tax price * r, and after-tax price = before-tax price + tax amount. For before-tax reverse solve, before-tax price = after-tax price / (1 + r), then tax amount is max(0, after-tax price - before-tax price). For rate solve, tax amount is max(0, after-tax price - before-tax price), and sales tax rate = tax amount / before-tax price * 100 when before-tax price is greater than 0; if before-tax price is 0, the app returns 0 percent instead of dividing by zero.

Sales Tax Calculator formula

This formula page covers the app's Sales Tax Calculator: a generic three-value checkout model for before-tax price, user-entered sales tax rate, sales tax amount, and after-tax price. It can add tax, remove tax from a tax-inclusive total, or derive an effective rate from before-tax and after-tax prices. It does not look up state, county, city, district, product, exemption, use-tax, shipping, marketplace, filing, or deduction rules.

r = R / 100; T = B * r; A = B + T; reverse before-tax: B = A / (1 + r); effective rate: R = max(0, A - B) / B * 100 when B > 0, otherwise 0

The calculator converts the entered percentage to a decimal rate, adds tax to a before-tax price, reverses a tax-inclusive total by dividing by one plus the rate, or compares before-tax and after-tax prices to solve an effective entered rate.

Symbol	Meaning	How this page uses it
B	Before-tax price	The price before sales tax, entered as Before tax price or solved from the after-tax total.
R	Sales tax rate	The entered or solved percentage shown as Sales tax rate. This app treats it as a user-entered assumption, not an official lookup.
r	Decimal tax rate	The sales tax rate divided by 100, so 6.5 percent is used as 0.065.
T	Sales tax amount	The currency amount reported as Sales tax amount.
A	After-tax price	The checkout total after adding the modeled tax amount.
D	Price difference	The nonnegative difference between after-tax price and before-tax price when solving the effective tax rate.

Step by step

Read Solve for to decide whether the calculator is finding after-tax price, sales tax rate, or before-tax price.
For after-tax price, divide the entered sales tax rate by 100, multiply before-tax price by that decimal rate to get tax, then add tax to before-tax price.
For before-tax price, divide after-tax price by one plus the entered decimal tax rate, then subtract the solved before-tax price from after-tax price to estimate the tax amount.
For sales tax rate, compare before-tax price with after-tax price, use max(0, after-tax price minus before-tax price) as the tax amount, then divide by before-tax price when before-tax price is greater than 0.
If before-tax price is 0 in rate-solve mode, return a 0 percent rate instead of dividing by zero.
Round currency and percentage outputs for display after the full-precision calculation.
Treat any real rate as something the reader must verify with the relevant state, local, or tax authority before using it outside this educational estimate.

Worked example

Default examples: add tax, remove tax, and solve an effective rate

The default calculator inputs use a $100 before-tax price and a 6.5 percent entered rate. That 6.5 percent value is an example assumption, not a current official rate for any location.

Convert 6.5 percent to 0.065.
Multiply $100 by 0.065 to get $6.50 of sales tax.
Add $6.50 to the $100 before-tax price to get a $106.50 after-tax price.
For a receipt-style rate solve, $80 before tax and $86 after tax has a $6 difference. Dividing $6 by $80 gives 0.075, or 7.50 percent.
For a tax-inclusive reverse solve, $107.50 divided by 1.075 gives a $100 before-tax price and $7.50 of modeled tax.
For the zero-rate fixture, $49.99 at 0 percent keeps the after-tax price at $49.99 and reports $0.00 of tax.

The formula explains the arithmetic relationship between before-tax price, entered rate, tax amount, and after-tax total. It does not prove what a retailer, marketplace, receipt, tax return, or tax authority will use.

Assumptions and what this calculator ignores

Geographic scope: works globally. The math is currency-agnostic, so enter amounts in your own currency; local taxes, fees, and product rules are not included.

The sales tax rate is an entered assumption. The calculator does not look up state, county, city, district, address-level, product, exemption, tax-holiday, shipping, delivery, marketplace, use-tax, seller-registration, filing, or deduction rules.
Currency values and percentages display to two decimals after full-precision math. Rate-solve mode floors a negative tax difference at 0, and the public input model accepts rates from 0 percent through 100 percent.
Scoped independent comparator checks pass 4 of 4 scoped fixtures for after-tax price, effective-rate solve, before-tax reverse solve, and zero-rate handling. That validation covers the same generic three-value calculator, not current jurisdiction-specific rate tables or tax law. Results are educational estimates, not financial, tax, legal, accounting, filing, consumer-rights, or personalised purchasing advice.

What this formula does not include

The calculator uses the rate entered on the page. It does not automatically choose state, county, city, district, destination, product, or address-level rates.
The default 6.5 percent rate is an illustrative calculator input, not an official current rate for a jurisdiction.
Real rates and rules should be verified with the relevant state, local, or tax authority. Examples of official sources include state revenue department pages, address-rate lookup tools, and local tax authority guidance.
The calculator does not model exemptions, product taxability, tax holidays, shipping or delivery charge treatment, coupons, rebates, environmental fees, marketplace facilitator rules, use tax, filing obligations, or federal itemized deduction treatment.
Retailer receipts can differ because of line-item rounding, taxable and nontaxable item mixes, discounts applied before or after tax, shipping treatment, local district taxes, or seller-specific systems.
Rate-solve mode uses max(0, after-tax price minus before-tax price). If the entered after-tax price is lower than before-tax price, the modeled tax amount and rate are floored at 0.
Rate-solve mode returns 0 percent when before-tax price is 0 to avoid dividing by zero.
The input schema allows entered rates from 0 percent through 100 percent. Values outside that range are not part of the public calculator model.
Scoped independent comparator checks currently pass 4 of 4 scoped fixtures for after-tax price, effective rate, before-tax reverse solve, and zero-rate handling. The validation covers the generic three-value calculator only, not jurisdiction-specific rate tables or tax law.
The result is an educational estimate from the entered assumptions, not financial, tax, legal, accounting, filing, consumer-rights, or personalised purchasing advice.

Common mistakes to avoid

Using an old, rounded, or statewide-only rate when the real transaction depends on state, county, city, district, address, product type, seller rules, or current tax authority guidance.
Mixing tax-inclusive and tax-exclusive prices. Label whether a number is before tax or after tax before using it in a receipt-style reverse solve.
Treating the output as a tax bill, final receipt answer, itemized-deduction answer, exemption decision, shipping-taxability answer, marketplace-rule answer, or legal conclusion. Official tax authority, retailer, marketplace, and legal sources can change the real result.

Key terms

Before-tax price: The price before the modeled sales tax amount is added. It is the base for the tax calculation in after-tax mode and the solved value in reverse mode.
Sales tax amount: The currency amount added by the entered sales tax rate. It is calculated from the before-tax price in forward mode and from the price difference in reverse or rate-solve mode.
Effective entered rate: The tax amount divided by the before-tax price. It helps explain a receipt, but it is not proof of the official rate or taxability rules used by a seller.

Frequently asked questions

What is the formula for sales tax?

Convert the rate to a decimal and multiply: tax = price × (rate ÷ 100), and the after-tax total is price + tax. With the calculator's default example, a $100.00 purchase at 6.5 percent produces $6.50 of tax and a $106.50 total. The full derivation, including the reverse and effective-rate forms, is documented in the formula section of this page.

How do I remove sales tax from a total price?

Use the reverse solve: before-tax price = after-tax total ÷ (1 + rate ÷ 100). For example, a $106.50 receipt total at a 6.5 percent rate backs out to a $100.00 pre-tax price. This is the calculation to use when a receipt or listing shows only the tax-inclusive amount and you need the base price for expensing, bookkeeping, or price comparison.

Does the calculator know my state or city sales tax rate?

No. You enter the rate, and the default 6.5 percent is an illustrative input, not an official rate for any jurisdiction. US sales tax is set by state, county, city, and special districts, and the combined rate depends on the delivery or purchase address and the product category. Look up your combined rate with your state's department of revenue, then enter it here.

How do I work out what tax rate I was actually charged?

Enter the before-tax price and the after-tax total, and the calculator derives the effective rate: (total − price) ÷ price × 100. This is useful for checking a receipt where multiple line items or a district surcharge make the rate unclear. If the derived rate looks wrong, part of the total may be a non-tax charge such as a deposit, fee, or tip, which this arithmetic cannot separate.

Does this work for VAT or GST outside the United States?

The arithmetic is the same three-value relationship, so it works as a generic estimate anywhere you know the rate. But VAT systems usually quote prices tax-inclusive and have their own invoicing rules, so use the dedicated VAT calculator on this site for net-price, gross-price, and VAT-amount solves - it is built around tax-inclusive pricing conventions.

Methodology, sources, and disclaimer

This calculator is an original three-value model linking before-tax price, an entered rate, tax amount, and after-tax total, with add, remove, and effective-rate solves each pinned by deterministic fixtures and rounding policy tests. It is not copied from a single source.

Fixtures pin the $100-at-6.5-percent default and the reverse tax-inclusive solve. The result remains an educational estimate, not an official rate lookup or a tax-authority determination for any jurisdiction.

Formula version 2026.05.22-generic-sales-tax. The version marks the calculation logic and validation fixture set used for this estimate.

State, local, or tax authority rate pages should be used when a real sales tax rate is entered.
Official examples include state revenue department guidance and address-level lookup tools such as California CDTFA sales and use tax rate resources or Washington Department of Revenue sales and use tax rate resources.
IRS sources are needed only if a separate page discusses federal itemized sales-tax deduction treatment; this generic calculator does not determine deductions.

Results are educational estimates, not advice. Read the full disclaimer.

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