As Mark Drela wrote here one time there is no difference between a regular wing and tail layout, a tandem wing and a canard. They are just different spots on a continuous line of transition from the one extreme to the other. So if you got different results from the two calcualtors you either entered the wrong or different information in one or the author of the calculators used a wrong equation in one of the applications.

Or it could just be some build up of tolerances. What where the results from the two calculators? Perhaps you could give us the measurements of your design and we can try it ourselves to double check?