Spending audit, 201601 May 2017
Mint tracks all of my spending. Mint automatically categorizes transactions into categories like “Pharmacy” or “Rental Car & Taxi”, and I periodically check and change Mint’s categorizations.
I exported the data from Mint and, using Pandas, assigned each transaction to categories that were less granular and more relevant than Mint’s categories, like “transportation” or “work expenses”.
Then I classified transactions into an even coarser set of categories, classifying transactions by their purpose, like “food,”, “entertainment”, or “charity.” But many transactions serve multiple purposes. For example, a $12 restaurant meal provides maybe $3 of food and $9 of enjoyment. An MBTA pass can get me to work and then to a party.
So I assigned some of the granular categories to multiple coarse categories. For example, I buy lunch at Harvard partially because I need to eat and partially so I can spend more time working instead of cooking, so I assigned ``work food” 50% to “food” and 50% to “work expenses.” I assigned restaurant spending 25% to “food” and 75% to “amusement.” However, it was impossible to assign a purpose to many transactions. Spending on transportation serves many purposes, so I just left it as “transportation”. Cash could have been used for anything, so I lumped it in with “unknown.”
I live with my husband in a one-bedroom apartment in Cambridge, MA. I’m a Harvard grad student. I earned money by teaching at Harvard in the spring, from Harvard for no reason in the summer, and from working part-time at a data science start up since the summer. 
I got married this year. The wedding cost less than $1000 , but people gave us money, and we actually came out ahead.
I bought an expensive laptop this year, which was by far the largest expense after food and rent. I also bought a lot of clothing, since I’m at a point in my life where I shouldn’t be wearing shirts from high school and ripped-up athletic shoes to work. I expect to spend less on clothing in the future. I spend a lot on convenience; since I’m paid hourly, it’s a better financial deal for me to buy an $8 lunch than to cook it, pack it, and clean dishes myself. I think I could save time and money by cooking a huge amount of food once a week and pre-packing lunches, but I can’t ever seem to make that work.
I made $46,572.50 this year. Since I’m filing jointly it’s hard to say what I paid in taxes, but it’s about $6,800, leaving an after-tax income of about $39,800.
My biggest expense after rent and taxes is usually charity, and I usually donate at the end of the year. I took the Giving What We Can Pledge several years ago: I’ve pledged to donate everything I make over $34,000 post-tax, and at least 10% of my income. ($34,000 in 2012 in 2012 dollars, $35,264 today.) That left me obligated to donate $3,757 in 2016. I donated my “2016 donation” of $14,400 to GiveWell in the beginning of 2017 rather than at the end of 2016 for tax reasons (and I’ll donate again at the end of the year, and call that my “2017 donation”). I’m not going to count that here, though.
Spending by category (granular)
|Category||Amount||Number of transactions||Average per transaction|
|books and magazines||170.57||19||8.98|
|software for education/work||167.73||4||41.93|
|wisdom tooth removal||141.80||1||141.80|
Spending by category (coarse)
|Coarse Category||Corresponding Granular Categories||Examples|
|entertainment||amusement, 75% of restaurants||Google play music, Felipe’s|
|wedding||wedding||venue, food, alcohol, music|
|self-improving entertainment||books, magazines, sports||The Economist, rock climbing, trail races|
|appearance||clothing, hair, appearance|
|education/work/professional development||laptop, website, 50% of work food, noise-canceling headphones, Stata|
|other necessities||coffee shops, other necessities, CVS||soap, instant coffee, phone|
|charity||charity||none (in 2016)|
|unknown||unknown, cash, other||ATM withdrawal|
|food||groceries, 50% of work food, 25% of restaurants||food|
|medical||wisdom tooth removal|
|transportation||transportation||Uber, bicycle repair, train|
|housing||rent, utitilities, home improvement|
This is a total spending of $27,408, or about $20,608 if you don’t count taxes. I usually spend about $18,000 a year, not counting taxes, so this was an average year before the new laptop. I used Betterment to invest the rest, putting as much as possible in a Roth IRA.
 I develop econometric algorithms. It’s a lot of fun. Ask me about it.
 Pretty good for 38 people if you ask me!