By the sounds of every other poster, I too having read the topic title I couldn't see what the problem was? Let's consider you eat three meals a day, if that ready meal (presumably an evening meal) is only 500 calories and the very generalised ultra average intake is about 2000 calories then you would need to make up another 500 for both lunch and breakfast and 500 from snacks in between.
The calories isn't the problem with ready meals, the high fat, salt and sugar content is.