About PercentOffCalculator

What this tool does

PercentOffCalculator is a straightforward discount calculator that computes the sale price from an original price and a percent off, plus the inverse — what percent off you're getting given a sale price and an original price. It's designed for shoppers who want to verify a sign or a coupon in a few seconds, without signups, intrusive ads, or anything fancier than the arithmetic itself.

How the math is verified

The calculator uses standard percent-off arithmetic — sale price equals original price times (1 − percent / 100) — implemented with BigNumber for precision so rounding doesn't drift on long decimals. Round-trip cross-checks confirm that solving forward and then backward returns the same inputs. If you spot an edge case that looks off (stacked discounts, unusual rounding rules at a specific retailer), please email and I'll take a look.

A note on appropriate use

This is straightforward shopping arithmetic. It doesn't include sales tax, shipping or service fees, store-specific loyalty rules, or stacked promotional discounts. For complex multi-coupon situations, walk through each discount step by step and apply this calculator at each stage rather than expecting a single number to capture everything.

About the author

Hi, I'm Jimmy Raymond. I built PercentOffCalculator as part of a small network of focused calculator sites that I've been maintaining for over two decades. I have a B.S. in Environmental Engineering and a B.S. in Computer Science from New Mexico Tech and the University of New Mexico, and my professional work has covered safety-critical aerospace and space systems, real-time embedded software, and full-stack web development.

The design philosophy here is the same one I bring to that engineering work: the formula has to be correct, the assumptions have to be stated, and the limits of the tool have to be honest. A discount calculator is a small thing, but a small thing done well still earns its keep.

Contact

Email me at aj@ajdesigner.com for corrections, feature requests, or general feedback. You can also find me on LinkedIn.

— Jimmy