Tax, Discount and Margin Calculator

Two things go wrong with money in a spreadsheet, and both look right on the page. Taking 20% off a gross figure does not give the net — £120 gross is £100 net, not £96, because the 20% was added to the net rather than taken from the gross. And splitting £10 three ways at £3.33 loses a penny, so the invoice does not add up. Everything here is held in whole pennies and both mistakes are checked for.

What to work out

Amount

In whatever currency you are working in.

Rate (%)

The tax, discount, markup or margin.

Your answer will appear here.

What this generator does

Converts the amount to whole pennies, does the arithmetic there, and reports the net, the tax or discount, and the gross — or, for a split, every share.

How to use this tool

Choose what you are working out.
Enter the amount and the rate.
Read the answer, with the arithmetic shown alongside.
For a split, each share is given so the parts add back exactly.

Understanding the controls

What to work out: Add tax, remove tax, take a discount, add a markup, work out a margin, or split an amount evenly.
Amount: The figure you have. Whether it is the net or the gross depends on which calculation you chose, which is exactly the distinction that goes wrong.
Rate: The percentage. For a margin this is the share of the selling price you want to keep, which is not the same as a markup on cost.
How many ways: For a split, between one and a thousand. Odd pennies are handed out one each rather than piled onto one share.

Common use cases

Taking tax off a gross invoice figure correctly
Adding tax to a net price
Working out a sale price after a percentage discount
Telling a markup from a margin, which are different numbers
Splitting a bill so the shares add back to the total

How this generator works

The parts must add up to the whole, and undoing the calculation must give back the figure it started from — adding the tax back to a net, or taking it off a gross — within the single penny that rounding costs. For a split, the shares are added up again and must equal the total exactly, with no share differing from another by more than a penny.

Randomness and fairness

Nothing is random. The same amount and rate always give the same answer.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

One tax rate at a time, with no rules for reduced or zero rates, or for which items attract which.
This is arithmetic, not tax advice, and it does not know any country's rules.
Rounding is to the nearest penny at each step, which is the common convention but not the only one a finance system may use.
No currency conversion and no currency symbol — the figures are unitless.

Privacy and your data

The arithmetic runs in your browser. No amounts are transmitted or stored.