Are $200 Sephora purchases rash, or can they be justified? In the world of girl math, cosmetics and other unnecessary purchases are no longer seen as superfluous, instead they are seen as investments whose costs can be rationalized by their number of uses. For example, instead of looking at a $200 perfume as a $200 debit, by assuming it can last for 200 days, the bottle is now only worth $1 per day! This rationalization of unnecessary purchases, known as girl math, reconstructs our perception of consumerism. 

While girl math has only recently become a trend on TikTok, it demonstrates the idea of consumption smoothing, a theory first introduced by Milton Friedman in 1957. Consumption smoothing states consumers can maintain a consistent standard of living by balancing consumption over time. Girl math applies this theory by distributing consumption of a good, and consequently its price, over its useful lifespan. By discounting future benefits, consumers can rationalize purchases by determining if their overall utility outweighs the current costs. 

Additionally, self proclaimed girl mathematicians on TikTok claim that refunds are a free source of cash. Of course, this advice is clearly not grounded in mathematical fact, but consumption smoothing can imply that the liquidity provided by a refund is more valuable than the purchased goods, ultimately stabilizing standard of living. This mental accounting trick categorizes past expenditures as “sunk costs,” entirely discounting the original spending and framing only the refund as being relevant.

Finally, girl math argues that the monetary cost of purchases like a daily matcha or coffee are not relevant if the happiness, used by girl mathematicians as a proxy for utility, generated from the purchase outweighs the cost. I too would gladly suffer the $7 opportunity cost in exchange for a better morning. Surprisingly, consumption smoothing agrees with girl math—small indulgences can maintain a balanced level of utility over time by filling in sudden dips in living standards.

Of course, girl math is merely a social media trend meant to poke fun at irrational consumers, but it is interesting how consumption behaviors shared on the internet can demonstrate economic theories produced decades ago. By depreciating the upfront cost of a good by its useful lifespan, individuals take advantage of the intertemporal choice they have and rationalize unnecessary consumption by considering future benefits, rather than current costs. This highlights society’s need for a sense of balance, both financially and personally, over time. 



References:

Garcia, Cardiff, et al. “Planet Money Summer School 3: Smooth Spending & the 401(k).” NPR, 11 Aug. 2021, www.npr.org/2021/08/06/1025476458/planet-money-summer-school-3-smooth-spending-the-401k. Accessed 8 Oct. 2024. 

Krueger, Dirk, and Fabrizio Perri. “Understanding Consumption Smoothing: Evidence from The U.S. Consumer Expenditure Data.” Journal of the European Economic Association, vol. 3, no. 2/3, 2005, pp. 340–49. JSTOR, http://www.jstor.org/stable/40004977. Accessed 7 Oct. 2024.

Westlake, Emeraude. “Girls Just Wanna Have ReFUNds: “Girl Math” can ease financial stress, but this social media trend could perpetuate a stereotype.” The Tower, 21 Oct. 2023, thebishopstower.com/5652/culture/girls-just-wanna-have-refunds-girl-math-can-ease-financial-stress-but-this-social-media-trend-could-perpetuate-a-stereotype/. Accessed 7 Oct. 2024.