Limitations to Calorie Math!
One of the biggest issues with traditional 'calorie counting' is the perception of it's accuracy. In reality calculating both the calories we burn and the calories we eat are guesstimates at best.
Calorie calculators that estimate BMR (basal metabolic rate) do so based on age, weight, height and sex, it does not know about how much muscle you have relative to fat or any individual variations in your metabolic rate. These factors make this a loose prediction rather than solid calculation.
Calculators allow you to select an 'activity level' from a list of 4-5 options. While this can give us a good ball park figure it's unlikely that every person who chooses "Lightly Activity" will be doing the exact same amount of steps and exercise each day. Obviously.
NEAT (non-exercise activity thermogenesis) is a fancy way of saying all the movement you do each day that isn't formal exercise. This even include things like fidgeting and subconscious movement. This contributes a significant amount to daily energy expenditure and varies massively between individuals (1). With this in mind when a calorie calculator tells you that you need 1987kcal a day to maintain your weight it's an estimate, not an exact figure.
Monitoring the calories we eat is even less reliable. Calorie labels on store bought products are legally allowed to be up to 20% out. So your 500kcal sandwich could have been anywhere between 400-600kcal (2). Our ability to accurately count calories is not great either and we tend to underestimate the amount we are eating (3).
So when we take all this together we can start to see how loose our ability to really know how many calories we're eating and burning is.This doesn't mean it's all a complete waste of time. Generally following a plan in line with a loose target is going to bring you to the right place for your goal, and you can always adjust up or down accordingly
It does however mean that obsessing over whether you had four or five grapes with lunch or if your salad was 498kcal or 510kcal is probably an unnecessary stress. This is why my quick-start nutrition plans and the majority of plans I create for clients round calories to the nearest 100kcal.
REFERENCES:
(1) von Loeffelholz (2018)
(2) FDA Food Labelling Regulatory Information
(3) Yanetz et al. (2008)