Base Metabolic Rate
The body needs a certain amount of energy just to keep the organs functioning even if you are in a coma and not moving at all. The number of calories required to maintain life is known as the Base Metabolic Rate (BMR).
This can be estimated using one of a number of formulae that have been tried, tested and adjusted over many years.
Your daily calorie requirement can then be estimated relatively accurately by multiplying your BMR by a factor determined by the type of activity or job you have.
Using the calculators
As an amateur athlete, there are some days on which you will train particularly hard, other days will be lighter and at other times there may be no training at all.
In my own case, I often do a three-hour cycle on a Sunday (3000 additional calories), Wednesday is fairly light with just an hours evening swimming session (750 calories) and Friday is my recovery day (0 additional calories).
It is important to ensure that I go out properly fueled on Sunday and take enough calories to recover for swim and run sessions on Monday. My schedule means my calorie intake should be:-
I have calculated my base metabolic rate adjusted it for my business activity, largely sedentary, and it comes to about 1800 calories per day.
I know from my TomTom watch how much I have burned on the different training days - and I have checked it against the various online calculators. The result is I know how many calories I must consume to maintain my weight.
One problem remains; it is difficult to consume 4800 calories in a single day when you also try to eat only 1800 calories on another day. This means that you must use the information with a certain amount of common sense and adjust your eating plans accordingly.