If you buy something for $5, it’s basically free. If you buy something and get a refund, that’s free money. If you spend $200 on a jacket but wear it 20 times, it actually only costs you $10. Welcome to girl math, the money trend we can’t stop talking about.

But what’s the deal? Is it a harmless bit of fun, or a sign of something more sinister? Frankly, I’m torn.

I’m a Financial Behaviour Specialist so, of course, part of me was always going to suck all the fun out of girl math within seconds of seeing people justify unnecessary spending. But I’m also a Millennial who will drive to KFC to save the $8.95 delivery fee and deem my popcorn chicken effectively free as a result. Consider me stumped.

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My own cognitive dissonance on girl math is demonstrative of the many different shades of the trend. On the one hand, considering refunds or $10 in an old coat pocket as ‘free money’ isn’t anything new. It’s actually a normal part of the way our brains make sense of money, known as mental accounting.

Girl math is based on mental accounting

Mental accounting refers to our tendency to treat money in different ways depending on where it came from or what it represents. If you get paid $1,000 from your employer as part of your normal wage, that money probably gets split between bills, savings, groceries and a small amount of leisure spending. If you won $1,000 out of the blue, you’re more likely to spend that on something more frivolous because your brain sees that money differently.

Girl math’s trivialisation of financial decisions risks minimising the progress we’ve made [...] and harks back to a time when women had to justify their spending [...] in a way that stripped them of their independence.

Personally, I find this lighter side of girl math quite enjoyable. Anything that highlights the silly little quirks of the human brain gets a robust chortle from me, especially with so much darkness in our social feeds. I embrace the side of girl math where getting a discount off my restaurant bill absolutely means I can order an extra dish (it’s basically free). And yes, I can absolutely help myself to the minibar at a hotel if I’ve earned cashback when booking (also basically free). But that’s where my love of girl maths runs out.

Women shouldn’t be seen as ‘bad with money’

Given that only 50 or so years ago, women weren’t allowed to have their own bank accounts, girl math feels like somewhat of a regression. Patriarchal gatekeeping of financial autonomy and economic opportunity created and cemented the stereotype that women and girls are bad with numbers and bad with money.