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Here's your money briefing from Monday, October 16th. I'm JR Whalen for the Wall Street Journal.

If you pay cash for something, do you consider it to be free? If something costs less than $5, do you round it down to zero and just call it a day? Some people do. And on social media, it's known as GirlMath.

They're trying to think about what is worth the investment or how can they stomach the amount of money that they're about to spend in a less painful way.

For some people, it is a joke and then for other people, it is really just justifying using money that they may or may not have.

We'll talk to Wall Street Journal reporter, Hobby Libre, after the break.

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Here's a list of things I firmly believe because of GirlMath. Anything under $5 is free. Anything I buy with a gift card is free. If I buy something but then I return it, I've made money.

The point to an event or a concert is free because I purchased the tickets so long ago it doesn't even count.

That's a clip from a TikTok creator summing up some examples of what can be considered GirlMath. It may sound like some fuzzy math, but it's actually a social media trend.

Wall Street Journal reporter, Hobby Libre joins me. So, Hobby, how does GirlMath work?

GirlMath is basically a slightly twisted logic where you sort of justify your spending habits. You can call it a cheeky way to consider a purchase.

For example, if you see a sweater, it was originally $100 and then you bought it on sale. The money that you saved from the sale difference you get to spend or you actually maybe even earned money and now you are there for a richer.

I spoke to another source who said that any time she goes into a store and she doesn't buy something, she walks out richer because she didn't spend the money and then she has that money to spend the next day.

So, money didn't actually grow in her pocket. It just didn't leave her pocket.

Correct. And the money is actually growing in her mind, which I guess is comforting to her.

So, who's doing this kind of math?

I'll say that the GirlMath hashtag started out on TikTok. The name was coined by a radio show in New Zealand. They called it GirlMath.

Just in response to all the trends that are happening on TikTok right now, like girl dinner and girl walks and so on.

And they created this playful segment where they would allow callers to phone in and talk about their purchases and then they would do math and back solve how they could either justify their purchases or maybe even how they're making money.

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