The "Girl Math" of Buying Beauty Products

On the heels of the popular girl-dinner trend, allow us to introduce to you: girl math. Popularized by TikTok user Samantha James, the concept pokes fun at bad spending habits by justifying them using some truly impressive mental gymnastics. "Anything under five dollars is pretty much free," James noted as an example of her girl math-inspired train of thinking. "Returned something at Zara for $50, bought something else for $100, then it only cost $50," she added as another. The thought process felt a little too familiar, especially if you're a lover of beauty products.

From the mini-sizes of products feeling like the ultimate steal to purchasing anything with points — there are many forms of "beauty math" out there. And while we test beauty products for a living, many POPSUGAR editors have found it especially makes sense when you're standing in a cosmetics store. "If I buy something on pre-order then it's free because I forgot about it," one editor said. "Anything under $10 at Sephora is free," said another.

The girl-math professor to beauty obsessive pipeline is real so in honor of the fun, the POPSUGAR Beauty team revealed all the times that our girl-math equations helped us to justify some of our favorite beauty purchases. From product returns basically being a savvy personal savings account to a long-held philosophy on store credit, read ahead on all the times that girl math really came through for us.

"If I make a return, get my money back, and then buy something at full price, it was actually free," — Ariel Baker, assistant beauty editor

"When I make a big purchase and I know I'm going to return some of them, I basically consider the money to be in a savings account until I make the return. I can't touch it but I know I'm getting it back, so I'm actually saving money," — Renee Rodriguez, staff writer and social producer

"Any gift set that gives you multiple products for the price of one is worth buying in bulk," — Kelsey Castañon, beauty director

"If a gift set includes samples and a voucher for a full-sized product, the entire thing is half price," — Ariel Baker

"Any travel-sized or mini product in the aisle before checkout is free," — Ariel Baker

"If you get a free sample with purchase at Sephora and use it all up, you're basically buying the full size at a discount," — Jessica Harrington, senior beauty editor

"If I pay in cash, it's basically Monopoly money so it was free," — Ariel Baker