Reverse Sales Tax Calculator
Extract the tax from a total that already includes it.
Rates change with budgets and local ballot measures, and the rate that applies depends on the delivery address and product category. Treat these as planning figures, not as a filing.
Price before tax
$100.00
$7.50 of tax inside the total
Going backwards means dividing by 1.0750, not multiplying by 7.5%. The wrong method overstates the tax by $0.56 on this one line — and it is wrong in the same direction on every line, so it compounds across a year of bookkeeping.
How the Reverse Sales Tax Calculator works
Going backwards from a total is where most people get tax arithmetic wrong. The tax inside a gross price is found by dividing by one plus the rate — not by multiplying the total by the rate. At 8.25% the wrong method overstates the tax by about 8% of itself, on every line, in the same direction.
Not financial advice. Marketplace fees change, and they vary by country, plan and seller status. Every rate here is an editable default, not a quoted price — check the platform's current fee schedule before you price a product against it. This is not tax or business advice.
Frequently asked questions
How do I find the tax inside a total?
Divide the total by 1 plus the rate to get the net, then subtract. At 8.25%, divide by 1.0825. Multiplying the total by 8.25% gives a figure that is too high, because the tax was charged on the net, not on the total.
How wrong is the shortcut?
It overstates the tax by the rate squared, roughly. At 8.25% the error is about 0.63% of the total; at 20% VAT it is 3.3%. Small on one receipt, systematic across a year of bookkeeping.
When do I need this?
Reconciling till totals, splitting a marketplace payout into net revenue and tax, expense claims, and any market where prices are displayed tax-inclusive by law.
Does the same maths apply to VAT and GST?
Yes, identically. The VAT inside a 20% gross price is one sixth of it; the GST inside a 10% gross price is one eleventh. The fraction is always rate divided by 100 plus rate.