You'll start to see a pattern as you progress. If you're the type that it won't bother and become an unhealthy obsession, you can track daily w/ notes, like, too much sodium, over calories, under calories, TOM, etc to see how it affects you in the beginning. I like seeing the visualization in spreadsheets 'cause that's how I am
If it bothers you or makes it worse, find another method.
I've found I know when my (inconsistent) period is going to start because I do bloat and can't lose an ounce and normally go up some. I'm lucky to hold steady during the period then at the end, which just so happens to be today
I get a whoosh! In one week, last Friday to today, I "lost" 2.5 from my pre-period weight; I didn't hit my calorie deficit as much as I would've liked so it could've been more if I were disciplined.
I also (TMI!) get slightly constipated during and slightly before my period so that doesn't help the scale at all!