I'm 4 1/2 months post-FIRE and what I miss most is the planning financially for FIRE. I realized today that I really miss the spreadsheets, calculations, planning for withdraws, checking numbers, calculating "what-if" scenarios, and so on. I'm of course enjoying no alarm clock/commute/boss, working on my own projects, doing the things I want to with my time, but I really do miss "messing with numbers."