This website has a "calorie calculator" - see the Training Tab/Running Calculators - which gives you an approximate answer. There are a variety of running books which provide formulae (plural because there are very material differences between men and women). That said, concepts such as "moderately active" are inherently subjective. If you are losing weight with the calories you normally consume, you are eating less than you need to maintain. Similarly, weight gain indicates excess consumption, but don't worry about small movements since internal fluid levels swamp day to day fluctuations due to fat storage or consumption.
I'm sorry there is no easy answer, or if there is that I don't know it.