Why do different cycling calorie calculators give out different answers, often multiplication of one with a fixed number?

Question

I’m overweight and trying to lose weight via diet and stationary cycling but I’m confused with different calculators

if

Stationary bike says 100 calories (no weight input)

online calculators say 200 400 600 etc asking me the same info including weight

In: 4

Answer 1

I belive I cud possibly maybe explain it bcus I have made a calorimeter ,maybe it wud be wrong but still..
Three main equations are used in these calculators
1.Miffflin St Jeor Equation
2.Harris Benedict Equation
3.Katch McArdle Equation
So the different answers maybe bcus of that q