Here are two planners that can help you figure out how quickly you're likely to lose weight at different levels of calorie restriction. They don't use the inaccurate 3500 calories = 1 pound formula. Instead, they take into account how your metabolism slows as you lose weight.
In the first six months after surgery, I lost weight more quickly than the apps indicated. (This may be due to the fact that WLS seems to "reset" your metabolism.) But they seem to be reasonably accurate about the rate at which I'm losing weight now.
https://www.niddk.nih.gov/bwp I suggest that you click on the settings menu at the upper right, and select expert view. Also, at the top of the left panel, there's an "Advanced Controls" setting that you can toggle on or off.
https://www.pbrc.edu/research-and-faculty/calculators/weight-loss-predictor/ This one is a bit harder to use, since you have to enter your calorie reduction per day instead of calories per day. My suggestion is 1) enter all the other information but leave the default for calorie reduction, then 2) look below the chart to see what it says your "current" calorie intake is (really, it's the amount of calories you need to maintain your current weight) , then 3) subtract your real daily calorie intake (e.g., 800) from the value you got in step 2, and enter that for "calorie reduction".
Of course, real weight loss follows a more stair-step pattern with spikes and plateaus. You won't get the smooth curve they show in those graphs. But I think they can give you an idea of how quickly you can expect to reach your goal.