I had a spreadsheet showing the value of a portfolio on various days, and I wanted to figure out the effective APY (annualized growth) between different points in time. After some chewing, I eventually came up with a reasonable formula using logarithms:
100 * (10 ^ (log10(valueend / valuestart) / ((dateend - dateend) / 365.24)) - 1)
Speaking of math, today is the point that's exactly halfway between Cat Lady's half-birthday and her sister's integer birthday. We're embarking on a two-day, six-stop mini-vacation that will take us to West Orange, NJ to explore Thomas Edison's lab, then to Freeport, NY out on Long Island to meet with her sister for dinner, then to a nearby AirBnB. Tomorrow we start with the San Gennaro Festival in Little Italy, then to see my brother and family on Coney Island, and my parents in Bridgewater, NJ.