https://www.active.com/fitness/calculators/calories for example.
The amount of calories lost per day = the metabolic rate from the calculator - the amount of calories you eat that day.
The amount of pounds lost per day is: burned calories (above) / 3500 (number of calories in a pound of fat).
After a couple months of measuring my weight daily and knowing exactly what my caloric intake was, I calculated my real average metabolic rate by doing the reverse.
total calories lost in a period = lbs lost * 3500
calorie burn (metabolic rate) = total calories burned + total calories eaten
The above is per period so I calculated the average values for the days in a month and used them.
I didn't exercise much so the basal metabolic rate was fairly close to my real burn.
