About Percentage Decrease Calculator
This site does one thing: turn a pair of numbers, an original value and a new one, into an accurate, clearly explained percentage decrease. No account, no paywall, no dark patterns around the result. Everything below is the reasoning behind how it's built and who it's built for.
Why This Site Exists
Percentage decrease is simple arithmetic, but it's arithmetic that a lot of pages get subtly wrong, dividing by the new value instead of the original, dropping the absolute value and silently flipping a rise into a fall, or burying the formula under ad units and a life story before the number ever appears. This site puts the calculator first, states the formula in full, and works every claim on the page through to a checkable number.
It's an independent reference tool, not a financial, medical, or scientific authority. The math is exact; how you apply it to your salary, your lab results, or your investment portfolio is a judgment call that belongs to you or your advisor.
How Every Formula and Example Is Verified
The single formula the whole site is built on is:
Every worked example on this site, the LED bulb, the revenue drop, the reference chart, the FAQ answers, is computed directly from that formula rather than written by hand and hoped correct. Before anything ships, each number is recalculated independently and checked against what the page displays, including edge cases: a zero original value, a negative original value, an original and new value that are equal, and results that come out negative (a rise, not a fall). If a page ever shows a number that formula doesn't produce, that's a bug, see Contact to report it.
Who This Tool Is For
Anyone who needs a percentage decrease and doesn't want to re-derive the formula from memory: a shopper checking whether a discount sticker matches the shelf price, a student working through a homework set, an analyst comparing quarters of different sizes, a lab tech normalizing a before-and-after reading. The worked examples and FAQ are written to cover retail, business, investing, population statistics, health, and science, because the same four steps apply to all of them, only the units change.
Free, Independent, and Fast
There's no sign-up and no paywall on any calculation. The page is built to load in a fraction of a second and to keep working with JavaScript disabled, the calculator still shows a correct, server-rendered result even before any script runs. This site isn't affiliated with any calculator brand, spreadsheet vendor, or financial product; if a comparison on this site favors one option over another, it's because the arithmetic favors it, not because of a partnership.
Spotted a Mistake, or Missing a Language?
If a number looks wrong, a translation reads awkwardly, or a formula on this site doesn't match your textbook's notation, that's worth hearing about. Visit Contact, corrections to worked examples and formulas are the fastest kind of feedback to act on, since they usually mean checking one calculation against the page.