Enter two numbers and the answer and formula appear here.
Percent questions differ by what you take as the base. Pick one of four questions, enter two numbers, and get the answer together with the formula so you can check it.
FAQ
Can I use it for consumption tax?
You can, but the tax and discount page fits better. It has the 10% and reduced 8% rates, a choice of floor, round or ceiling for fractions of a yen, and the reverse calculation from a tax-inclusive price. "B% off" here does not round at all, which is not enough to produce an invoice figure.
What about two discounts stacked?
Apply them one after the other. "30% off, then a further 10% off" is not 40% off but 37% off, because 0.7 x 0.9 = 0.63. Put the first answer into the second calculation as the list price. Stacked coupons and member discounts trip this constantly, and the real discount is always the smaller one.
The answer came out negative.
In "percentage change", an after value smaller than the before value is reported as a negative percentage: 100 to 80 is -20%. That is the correct notation; write it up as "a 20% decrease".
What if the base is zero?
The calculation stops and says so. Growth from a base of zero is not mathematically defined, so nothing like "an infinite increase" is displayed. When comparing against a month with zero sales, the absolute difference communicates far better than a ratio would.
Are the numbers I enter stored?
No, and nothing is sent. It all happens in the page and is gone when you close the tab.