According to the NHS website men need around 2500 calories a day and women need around 2000 calories. But how accurate is this information?
How many calories an individual needs is very person specific. Using the numbers specified by the NHS, in my experience most inactive people would probably find they will gain unwanted body fat on those calories. Some people need to earn the right to eat a lot of food. You earn that right by increasing your muscle mass which increases your metabolic rate allowing you to eat more calories.
So how many calories should you eat? The best way to work this out would be to record how many calories you eat over a 5-7 day period. Calculate the average and this will be your starting point consume these calories over a week or so and keep an eye on your weight. If it stays the same then you have found what we call is your maintenance calories. From here it's simply a matter of I'm reading your calories if you want to gain weight or reducing them if you want to lose some.
Aways there is never a one size fits all approach. Try this and let me know how you get on