Forward: the price times the rate, nothing clever
Adding sales tax is the arithmetic everyone thinks they know: $100 at 8.25% becomes $108.25 because 100 × 0.0825 is $8.25. The two details that trip people up: first, the rate that matters is the combined state-plus-county-plus-city rate at the delivery address — Texas’s 6.25% state rate becomes 8.25% in Houston once local layers stack. Second, taxable base: most states tax shipping when the item is taxable, but services are largely untaxed in most states (with real exceptions — Texas taxes many services, New Mexico taxes nearly everything). The rate field stays editable for your exact locality because rates are hyper-local — two ends of the same county can differ by a full point.
Reverse: pulling tax out of a receipt
The reverse direction divides instead of adds: a $108.25 total at 8.25% contains $8.25 of tax because 108.25 ÷ 1.0825 × 0.0825 = $8.25. The classic error is multiplying the total by 8.25% — which gives $8.93 and double-counts tax that was already inside the total. Reverse mode exists for real workflows: a freelancer backing the deductible tax out of receipts for a home office purchase, a reseller splitting an invoice into cost basis and recoverable tax, or an eBay seller verifying marketplace-collected tax did not come out of their pocket. The result rows show net price, tax amount and gross total so the three-way reconciliation is visible at a glance.
The 2026 state rate map, briefly
The highest combined rates cluster in the South and West coast: Louisiana’s average combined rate tops 9.5% with some parishes over 11%, Tennessee and Arkansas average near 9.5%, and Washington and California sit around 9%. The floor: Delaware, Montana, New Hampshire and Oregon levy no state sales tax at all — and Alaska has no state tax, though many of its cities levy local sales taxes. Destination-based sourcing is now nearly universal: tax follows the ship-to address, not your office. For an online seller the practical 2026 reality is economic nexus — after South Dakota v. Wayfair, virtually every marketplace and most small sellers collect where sales exceed $100,000 in a state, which is why marketplace payouts show tax line items you never remitted yourself.
What is taxable keeps shifting
Three 2026-relevant categories to check against your state: groceries are exempt or taxed at a reduced rate in most states but fully taxed in several Southern grocery-tax states; clothing is exempt in a handful of states (Pennsylvania, New Jersey, Minnesota) and taxed elsewhere, with New York exempting only under $110 per item; and digital goods — streaming, e-books, SaaS — have converged on "taxable in roughly half the states" with definitions that drift annually. If you sell across state lines, the safe 2026 posture is: collect by destination address through a marketplace or tax engine, and treat any "my state doesn’t tax X" instinct as a hypothesis to verify, because the exceptions are exactly where audits grow.
A worked example resellers actually need
You buy a vintage amplifier in-state for $400 plus $33 tax (8.25%) and resell it for $900, with the marketplace collecting 8.25% buyer-side sales tax on the sale. Your cost basis is $400 — the $33 purchase tax is not part of basis if you paid it as a consumer, which is why holding a resale certificate matters: with one, you pay $400 flat and the basis math is clean; without one, that $33 is a sunk cost that quietly worsens margin. On the $900 sale the marketplace remits $74.25 of buyer tax that was never yours, and your fee-bearing revenue is the $900 gross. The takeaway this calculator supports: net price, tax and total are three separate numbers — resellers who treat the receipt total as "the cost" misprice inventory by the tax rate itself.
Estimates for planning only — not tax, legal or accounting advice. Your actual return depends on facts this tool does not ask about. Figures are based on IRS Revenue Procedure 2025-32 (tax year 2026), verified October 2026.