Still fairly new to the game, about 2 years in on darkroom printing, I put some white electrician's tape on the bottle, write the date of mixing on it and I mark the number in equivalent of 8x10" sheets (eg 2 sheets of 5x7 count as 1 sheet of 8x10) of paper (or number of films in case of film dev) on it. The datasheet of the chemical usually states the yield per liter and this tells me when it's time to make fresh chemicals.
Paper dev I usually use max 2-3 sessions over 2-3 weeks time, or the maximum amount of sheets as stated in the datasheet (whichever comes first). After that I mix it fresh.
Or whenever I want the best possible quality for a print, then I always mix paper dev fresh.
Fix can go a long time AFAIK, so do the same thing (count sheets) and use it up to ~3 to 4 months max. Fiber based sheets count for 2 sheets (read that somewhere in a datasheet, don't exactly know why).
My films are always developed one shot and I use water as stop but fix for films I also re-use for several films according to the datasheet of the fixer.