If you’ve spent even ten minutes on TikTok in the last year, you’ve probably heard of Girl Math. It’s a trend where people (mostly women, let’s be real) use silly mental rationalizations to justify spending habits: “It’s basically free if I paid in cash,” “If I return something for store credit and use that later, I didn’t spend anything,” or “Concert tickets I bought months ago? It’s practically free now.”
Although it started as a joke, Girl Math really uncovers a lot about how our brains work—and it turns out that some of the psychology behind it is accurate. So, is Girl Math just funny TikTok logic, or is it backed by science? Let’s talk about it!
What is girl math, psychologically?
At its core, Girl Math is a lighthearted take on how we justify spending. It reflects common cognitive biases that affect everyone (not just girls), but this trend just happens to package them in a relatable, funny way. Here are the real psychological principles at play:
1. Mental Accounting: Coined by Nobel Prize-winning economist Richard Thaler, mental accounting is when we treat money differently based on where it came from or what we mentally assign it to.
- Example: You spend a little extra using your refund—even though it’s still money—because it “doesn’t count.” → Girl Math: “It’s store credit, so it’s not real money!” vs. psych reality: you’ve made a new “mental account” for that credit, so you feel freer to spend it.
2. Sunk Cost Fallacy: This bias is when we continue investing time or money into something just because we already put something into it—even if it no longer makes sense.
- Example: You bought a $40 yoga class bundle but don’t like it, yet you force yourself to go “so it’s not a waste.” → Girl Math: “I have to go to that brunch—I already bought the outfit” vs. psych reality: you’re trying to recover sunk costs, but that outfit money is already gone.
3. Present Bias: We happen to prioritize short-term rewards over long-term benefits. Basically, your brain loves now more than later.
- → Girl Math: “I’ve had a long week—I deserve this latte/tote bag/Target run” vs. psych reality: your brain sees immediate pleasure as more valuable than future savings.
4. Confirmation Bias: This one hits when we seek out or interpret information in ways that support what we already want to believe.
- → Girl Math: “If I skip four coffee runs, that basically pays for this $50 top” vs. psych reality: you’re building a logic ladder to back the purchase you already emotionally committed to.
Why it’s not (totally) a bad thing
Here’s the twist: Girl Math isn’t just financial denial. Sometimes, it’s actually a way to cope with decision fatigue, money stress, and the constant pressure to be hyper-rational with every purchase—especially for women.
It can be:
- A form of emotional regulation
- A way to assert control over your money
- Even a little form of self-care
Also, let’s not forget that men do this, too—they just don’t call it Boy Math. Ever heard a guy justify a $300 gaming console because it “only costs $0.82 per hour” if he plays enough?
The bottom line is that Girl Math is funny because it’s real—we all do it in some way. But behind the nervous laughs are real psychological biases that shape how we think about money, time, and our own self-worth. Girl Math flips the script that states that women may feel guilty when it comes to finances. It says, “I don’t need to be perfectly logical to enjoy things.”
Understanding them won’t stop you from impulse-buying something for a little serotonin at Ulta, but it might help you be a bit more aware of when your brain’s doing math…it isn’t actually math.