I love spreadsheets. Spreadsheet programs like Microsoft's Excel, Apple's Numbers and Google Sheets are the secret heroes of our civilization.
I've also been interested in personal finance and the FIRE community for a while—not so much in the early retirement aspect but in the financial literacy it teaches its members. I have combined my passion for both into one mega-spreadsheet that I use to track my income, expenses, savings and investments in one overview. While creating this spreadsheet I got proficient in some new formulas, which I'll share here—and also write down for my own reference.