[sannee]

Calculate? No. But you do not need to calculate, you can measure it indirectly, by running something like:

    X ← 2000
    while true:
        eat X kcal/day for about two weeks
        if your weight has increased: 
            X ← X - 200
        if your weight has decreased:
            X ← X + 200

Observe that this can also be modified for gaining/losing weight. It is also robust --- X actually need not be physically accurate, it is just a number in our calorie tracking app, so even if we are miscounting something, we are hopefully doing so consistently over time.