A sales tax calculator answers two shop-floor questions that look similar and are not the same sum. Add tax starts from a price before tax and puts one flat rate on top. Extract tax starts from a price that already includes tax and splits it into the net amount and the tax that was inside it. You type the rate. The page does not store a VAT table, a GST table, or a default of 5, and it does not say that the rate you typed is the legal rate anywhere.
The Percentage Calculator can tell you what 10 percent of 100 is. It does not round a tax line to cents and then build the gross price so the two displayed lines add back to the gross. That add-back is the reason this page exists. A discount is a different job again: it subtracts a percent from a sticker price. This page never treats tax as a discount.
Both modes stay in the browser. The amounts you type are not uploaded. Clearing the form removes them from the fields. The page is still not a checkout, an invoice, or a filing worksheet.
Enter in a field runs the same action as Calculate. A third decimal on the money, or a fourth decimal on the rate, is rejected instead of being silently shortened.
Add tax: tax = net × (rate ÷ 100). That tax is rounded half away from zero to cents. Gross = net + the rounded tax. Extract tax: the unrounded tax is gross minus gross ÷ (1 + rate ÷ 100). That tax is rounded the same way, and net = gross − the rounded tax. In both modes the displayed net plus the displayed tax equals the displayed gross. A rate of 0 leaves the tax at 0.00. An amount of 0 leaves every line at 0.00. A rate of 100 is allowed in extract mode: the tax is half of an even-cent gross, with a half-cent remainder rounded away from zero.
Half away from zero means 1.005 dollars of tax becomes 1.01, and the same distance below zero would move away from zero too. These tools do not produce a negative tax. The rounding is for the formula on this page. It is not a bank statement, a till reconciliation, or a tax-authority rounding rule for a particular country.
Net 100 at 10 percent: tax 10.00, gross 110.00. Gross 110 at 10 percent: net 100.00, tax 10.00. Net 80 at 0 percent: tax 0.00, gross 80.00. Gross 200 at 100 percent: net 100.00, tax 100.00. Those pairs add back. A rate of 10.125 percent is accepted because it has three decimal places. A rate of 10.1254 is rejected. Money of 19.999 is rejected because it has three decimal places.
Add: tax = 100 × 0.10 = 10.00; gross = 110.00
Extract: tax inside 110 at 10% = 10.00; net = 100.00The arithmetic runs in the page. There is no account, no saved history, and no network call to fetch a rate. Do not type an account number or a customer list into the fields. The numbers exist only until you clear them or leave the page.
Type the rate yourself. This page does not look up a country rate. Tax is rounded half away from zero to cents, then net plus tax equals gross. That is display rounding, not a bank statement.
No. You type the rate. The calculator does not ship a country table and does not treat any rate as the legal one.
The tax is rounded to cents first. The other money line is the gross minus that rounded tax, or the net plus it, so the displayed lines add back.
Yes. A 100 percent extract splits an even-cent gross in half. A half cent of tax rounds away from zero, and the net is whatever remains so the lines still add up.
Only the add-on-top case is close. Extracting the tax already inside a price is a different formula, which is why it has this page.
