The core formula
For a taxable purchase of 80 with a combined sales-tax rate of 8.25%, tax is 6.60 and the total is 86.60. The taxable base may be different from the sticker price when items are exempt, shipping is treated differently or coupons affect the tax base.
Worked example
A $100 item at 8% tax has $8 tax and a $108 final price.
How to add sales tax
- Confirm the applicable tax rate for the product, customer and jurisdiction.
- Convert the percentage rate to a decimal and multiply it by the taxable price.
- Add the tax amount to the pre-tax price to get the final total.
- For multiple identical items, apply quantity consistently to the taxable base or final amount.
Tax rate and taxable base both matter
The arithmetic is straightforward only after the taxable amount is known. Discounts, shipping, exemptions and product categories can affect the taxable base depending on local rules.
When reversing tax from an inclusive total, divide by one plus the tax rate. Subtracting the percentage directly from the tax-inclusive total gives the wrong pre-tax amount because the rate was originally applied to a smaller base.
Common mistakes
- Applying the rate to a price that is already tax-inclusive.
- Subtracting the tax percentage directly when reversing an inclusive total.
- Using a rate from the wrong jurisdiction or product category.
Use the calculator
Add or remove sales tax using any custom rate, with quantity support.
Open Sales Tax CalculatorCombine the applicable rates before calculating tax
For a taxable purchase of 80 with a combined sales-tax rate of 8.25%, tax is 6.60 and the total is 86.60. The taxable base may be different from the sticker price when items are exempt, shipping is treated differently or coupons affect the tax base.
US state and local rate differences
A state base-rate preset does not give a final checkout rate. City, county and special-district taxes may apply, and some jurisdictions use destination-based sourcing. Check the transaction address, taxable product category and effective date before treating a calculated estimate as an invoice amount.
Frequently asked questions
How do I add 8% sales tax to $100?
Tax is $8 and the final total is $108.
How do I remove tax from a tax-inclusive total?
Divide the inclusive total by 1 plus the tax rate as a decimal.
Does CalcMetrio know the correct local tax rate?
No. You enter the rate. Verify the rate and taxable base under the rules that apply to the transaction.
What should I verify about uS state and local rate differences?
A state base-rate preset does not give a final checkout rate. City, county and special-district taxes may apply, and some jurisdictions use destination-based sourcing. Check the transaction address, taxable product category and effective date before treating a calculated estimate as an invoice amount.