How the reverse sales tax calculator works
Why division and not subtraction
If price × 1.0825 = total, then price = total ÷ 1.0825. Subtracting 8.25% from the total computes a different (smaller) number, because the tax was calculated on the pre-tax price, not the total. The error is proportional to the rate — trivial at 2%, $40+ on a $5,000 invoice at 8.25%.
Who actually needs this
Reimbursement reports (the receipt shows the total; the policy reimburses pre-tax), business expense bookkeeping (sales tax is often a separate deductible line), budgeting in tax-included countries (UK VAT, EU rates), and anyone comparing a tax-included price against a tax-added quote.
VAT vs sales tax, one paragraph
Most of the world uses VAT/GST — baked into the displayed price (a £100 item includes 20% VAT: £83.33 price + £16.67 tax). The US sales tax model adds tax at the register instead. Reverse-calculating works identically for both: divide by (1 + rate) to find the pre-tax base.