This. There is no way I can know my exact precise calorie count, just like I can't know my exact calories burned in the day. How ever calorie counting apps and things like my fitbit give me a good ballpark figure to work with.  Sure I might burn 3000 to 3500 calories a day, 3000 on a slow day 3500 on my exercise days. But it's never exactly those figures. But my diet has me eating 1800 calories. Do I eat exactly 1800? No almost certainly not. But I'm with in plus or minus 20% of that figure. So at any given day my deficit is always 1000 or better calories.  When I was maintaining my weight it was super easy, and the second I go on my diet and put myself at a caloric deficit I start losing weight by the end of that week.