When on a diet you need to eat 500 calories less right?
And this is really down to one key reason...
If you are only a small person, i.e. don't weigh much, 500 Calories for you, as a small person might be too much and be too extreme a diet.
And extreme diets in ANY context are hard to stick to.
Consistency is key when dieting, sustainability.
Creating a small calorie deficit of around 5-10% is best, this is manageable and sustainable and will aid in a consistent fat loss journey.
So always calculate your calorie intake based on your body weight.
So work out where you are, then eat 5-10% less, and if nothing happens for 2 weeks drop another 5%, don't go for a big drop in calories right at the start, do it gradually.
The best diet is the one you will stick to!