Sales Tax Calculator
Calculate sales tax to add to a purchase subtotal or reverse-calculate pre-tax amounts from a grand total.
Last verified: September 2026Inputs & Parameters
Calculation Results
Sales tax rate is fully editable. Tax rules vary by local state, county, and city jurisdictions.
Forward and Reverse Sales Tax Computation
Sales tax is a consumption tax imposed on the sale of goods and services. A sales tax calculator provides two essential accounting operations: adding tax to a net subtotal (Forward) or extracting the taxable subtotal and embedded tax from a gross receipt (Reverse).
Core Mathematical Formulas
- Add Sales Tax (Forward):
Tax Amount = Subtotal × (Tax Rate / 100) - Gross Total:
Total = Subtotal + Tax Amount = Subtotal × (1 + Tax Rate / 100) - Extract Subtotal (Reverse):
Subtotal = Gross Total / (1 + Tax Rate / 100) - Extract Tax Paid:
Tax Amount = Gross Total - Subtotal
Worked Example
Calculating tax addition on an $85.00 subtotal at an 8.25% sales tax rate:
1. Tax Amount = $85.00 × 0.0825 = $7.01
2. Gross Total = $85.00 + $7.01 = $92.01
3. Reverse Verification: $92.01 / 1.0825 = $85.00
Assumptions & Limitations
Sales tax rates vary across municipal, county, and state/provincial boundaries, and exemptions frequently apply to basic groceries, prescription medications, or wholesale transactions. Always verify applicable statutory local rates.