'I just discovered 'Girl Math,' and now everything makes sense.'

It's a handbag, and it's $300. It's simply too much money for a handbag during a cost-of-living crisis.

Or is it?

What if you're going to use that bag every work day, plus on weekends, plus as an overnight trip bag, plus as carry-on when you're travelling? It's multi-purpose. You'll have it for ages. It means you won't buy three shitty bags that keep falling apart. 

You do the maths. 

Over just one year, that $300 bag is really only 80 cents per day. Which is practically FREE. You might say you actually MADE money by purchasing the bag.

Financial advisors are screaming. 

Economists are shaking.

That's not how it works, they say. You simply do not need the $300 handbag. 

But it's Girl Math. And it's bulletproof. 

Want to read more? Check out Elfy Scott's case... against (sort of) Girl Math.

I first came across this concept on TikTok, via a video from New Zealand radio show Fletch, Vaughan & Hayley. In one example, a woman named Andrea rang in, sharing that her hairdresser had told her she'd look great with some hair extensions for her wedding – at a cost of $400. But could she justify the cost?

@fvhzm #girlmath ♬ original sound - FVHZM

Host Hayley explained that if Andrea chose to save the $400 now, she'd look at the photos and always know she could've had extra strands of hair on her head. It would eat away at her for 10 years. So much so that she'd need to redo her wedding to get new photos, at which point we're looking at $40,000. So spending the $400 is ACTUALLY saving Andrea $39,600 in the long run. Wow. Flawless Girl Math.


A producer on the show did further calculations to demonstrate Andrea was really only paying $1.40 per inch of hair and honestly, what a bargain. 

"That's basically free," was the sentiment. "You're earning money."

Try to argue with it because you absolutely cannot.

I realised I'd been doing Girl Math forever. In the days leading up to my wedding, I called my sister in a frenzy. I'd found a dress online that I wanted to wear for my reception, but I just didn't know if I could justify spending any more money when I had already spent more money than I'd ever spent on anything.

The reception dress was $500. Who has $500? No one has $500.

"You need to buy it," my sister said, exasperated by how obvious the Girl Math was.

"Imagine looking back and always wondering. You actually need to buy the dress to ensure the rest of your money is well spent.

"Plus you could resell it or rent it out, in which case it’s literally free. You could even make a profit."


It made perfect sense. It was Girl Math.

I bought the dress, loved it, and resold it a few weeks later for $400. So really, it was a $100 dress, and if you divide that per wedding photo – photos I'll have for the rest of my life – it was literally $1 per photo. Which, according to my calculations, is dangerously close to free.

When I tentatively asked about Girl Math in the Mamamia office, wondering if perhaps my New Zealander friends and I were the only ones who engaged in this economic principle, there was unanimous support. 

"Not sure if this counts," said one colleague, "but in my mind, if I paid in cash it was free."

Of course that counts. It's one of the fundamental tenets of Girl Math. 


Listen to the full breakdown on Mamamia Out Loud. Post continues below.

If you paid in cash, it was either no longer in your bank account or it never went into your bank account in the first place. Hence, it's free money. 

Also, any money spent at an airport isn't real. Don't ask me why. I don't make the rules.

Getting an Uber is hugely favourable among Girl Math advocates, because: 

a) If you don't have a car, it means you're literally saving money on insurance, rego etc by getting Ubers instead;

b) If you do have a car, you're saving money from the inevitable fines you'd get if you were driving (perhaps this only applies to... me).

If you get public transport, like wow. You're pretty much earning money and actually owe yourself a ~$20 treat. 

Another colleague explained:

"If I am looking at buying something for $60 online and shipping is $20, but I get free shipping if I spend $100, then I am definitely spending $100 – and in my head, I saved $20 on shipping, because even though I spent an extra $40 to get to $100, I got a tangible product for that, whereas to me shipping is intangible and I get nothing from it."

Show this to Australia's leading economists. Explain it to our Treasurer. Paying to get an actual thing (e.g. a $40 top I didn't want) is far superior to paying half that for an invisible thing (e.g. shipping). It's logic. It's math. It's Girl Math. 


"A Thermomix pays for itself!" shouted one woman. "It's actually free!" she insisted, referring to the $2,579 appliance sitting in her kitchen. 

And don't even get me started on free samples. Will I spend money on a product I don't need in order to receive a package of samples I won't use? Obviously.

As this discussion unravelled, one lone man sat stunned.

But Sir.

While you may not understand the chaotic principles of Girl Math, would you like me to interrogate some of your purchases???

A golf club membership so you can literally go for a walk with your friends? 

Absurdly regular $30 haircuts that I've never noticed, not even once?

An expensive car with a big (?) engine (??) for literally no reason?

A fancy watch? When no one has needed a watch since the late 19th century?

In this economy, we need Girl Math. And the logic is foolproof, every time. 

For more from Clare Stephens, you can follow her on Instagram.

Feature image: Supplied.

Calling all Homeowners! Complete this short survey now and go in the running to win one of four $50 gift vouchers!