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Explaining Girl Math: How to Justify Your Big Purchases

girl math tiktok

This article was written by The Zillennial Zine’s fall editorial intern Elizabeth Miller. Find them on Instagram at @Lizzy_7979. If you would like to share an article with The Zillennial, send us an email at

This August, “Girl Math” has become a trending topic of discussion on TikTok. A New Zealand podcast and radio show group, @FVHZM, posted about the subject in late July. After the subject became wildly popular, they added a segment to their show justifying women’s purchases using girl math. Fans of the segments and users of girl math have bonded to create a new side of TikTok, girl math TikTok, to expose and discuss their logic. But this isn’t the first time a trend has tried justifying big purchases. Around this time last year, the “money will come back” trend was making its rounds on TikTok.

If you’re confused about what girl math is, or have a hard time following along with girl math logic, here is a simple guide to understanding the line of thinking in girl math. These are some of the most widely accepted rules to the girl math lifestyle.

As a disclaimer, this article is not meant to be financial advice, but if you happen to drop $300 at Sephora after this we won’t judge.

What Is Girl Math?


Big fans of girl math 🫶💁‍♀️ #girlmath

♬ original sound – FVHZM

Girl math is used to justify purchases and spending on a wide variety of things. The bank account is at the center of girl math, it is the home base. Additions and deductions come from the bank account. When some using girl math says they have “gotten money back” or are “up” or “down” with money, they are referring to spending money (often through a credit card) from their bank account.

Emotions and planning are also an important part of the logic of girl math. Planning to spend money and actually spending money are closely related and almost considered the same thing in many circumstances. The emotional value of a purchase can increase or decrease the monetary value of the purchase as well. A huge example of this is how cash withdrawals and preloading cards are treated (more on this later).

One last part, which deals with the actual math in girl math, is the timing and predicted number of uses for purchases. This is where you would consider if season affects your purchase and how you can get the most out of the item. 

So, let’s get into the rules!

Cash and Preloaded Cards Are Free Money

According to girl math TikTok, cash and preloaded cards are considered free money. This means that cash purchases and anything that uses a rewards card or a preloaded card through an app are not considered losses in the moment.

Why? This is because the emotional response of paying for these things has already happened. It’s hard to remember that feeling you had two weeks ago when you reloaded another $25 onto your Starbucks card. The same goes for withdrawing cash. The deduction from the bank account already happened, so there’s no need to feel guilty about spending it now. This means that cash, gift cards, and preloaded cards are free money! It’s a nice surprise to find them when you’ve forgotten about them, especially since they are not considered in the total balance with the bank account.

When And How You Make Money Back For Purchases


Absolutely no point in keeping this money bc its free🤗

♬ original sound – LUCY

There are certain circumstances in which you “make money back” so you can spend it on something else. The main categories these times apply to are returns and planning. Here is an example for returns: Say you’ve purchased a pair of shorts for $30, but they just didn’t fit right so you return them. Because you’ve already emotionally invested in spending $30, you have made back $30 and can go spend it on something else.

Something very similar happens for planning. Here are a few examples: You and a group of friends plan to go out for dinner and drinks on Saturday. At the last minute, plans have to be canceled. Because you were already planning to spend a certain amount of money (go ahead and be generous about this number), you can justify spending that much on something else instead.

You see a cute outfit in the mall that you want to buy, but you end up deciding not to get it. Let’s say the outfit cost $80. Since you did not spend the $80 on that outfit, girl math says you’ve made $80 back and can go spend that much on something else!

Emotional investment in these situations counts as spending money, so when you don’t literally spend, you gain money. The main idea is, you can justify your purchase if you were thinking about spending money anyways.

When And How A Total Price Is Lowered To Justify A Purchase


#girlmath is here to stay! Let us know if you need help justifying your purchases 😇

♬ original sound – FVHZM

There are also many ways to justify a purchase by “reducing” the price through girl math. A literal way of reducing the price is using rewards, coupons, and buying items when they are on sale. But, other elements can be applied to further reduce the price. The most common method is considering time and number of uses. When are you making the purchase? When will use the purchase? How many times will you use the purchase? Considering these questions can help lower the price (or at least your buyer’s remorse).

For example, say you want to invest in a fancy $600 espresso machine that has a lot of attachments. You’ve considered making this purchase because it was recently your birthday and you want to start making coffee at home. Birthday money can be considered free money, if you remember from earlier, reducing the price. The model you found was recommended by an influencer, who has a discount code if you use their affiliate link. Great, that lowers the price even more! And, fall is coming around, so the weather will be getting colder, giving you even more reason to make hot drinks with the machine. For the next months, it is foreseeable that you will use the machine frequently because you like coffee. Your usual drink out costs about $4, so, using girl math, you can find out how many times you would have to use the machine to have paid $4/drink at home. Divide the total cost ($600) by the average price of your drink ($4). This means you need to use the machine 150 times, to put that in perspective, if you use the machine every day starting September 1st, the machine will be paid off by the end of January. You could even further reduce the price considering what you’d save in gas by not going out.

But what other methods are there? Think about the sentimentality. Continuing with the example, maybe you foresee yourself having friends over and making drinks for everyone, or learning from your Italian grandmother how to make the perfect cappuccino. Those just make the purchase even more worth it, right?


somehow it makes sense #girlmath 🤷🏼‍♀️

♬ original sound – kenna 📚🍷

Or, perhaps, you want to justify a big purchase for an event, like a wedding. Investing in something for a sentimental event certainly lowers the price of its emotional value alone. And, if there is potential that not spending now will cost more in the long run, you could say you’re making money by investing early. Maybe you want to go with a slightly more expensive photographer for the wedding. If you don’t go with the nice photographer and you end up not liking the photos, you might have to spend even more money on another session with another photographer. That sounds like a costly nightmare!

And last but not least, what other services could apply to the purchase that you could deduct from the price? Maybe the photographer you want to go with offers props and backdrops. That would cut the cost of buying them separately, so consider that in the final cost!

So that’s the basics of girl math! Now you can keep up with girl math TikTok. What do you think about girl math? Let us know in the comments down below!

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