That makes sense. I did not realize that there were 3 different accepted algorithms for determining bitterness.
I am not sure what BeerCalculus uses, but I looked at TastyBrew and they also use Tinseth. I just tried their bitterness calculator and it was in the same range as Beersmith (about .4 IBU difference with same OG), but their recipe calculator is giving me way different IBUs. I used the same OG in the recipe and bitterness calculators. Guess their recipe calc is just off when it comes to determining bitterness.
Anyway, thanks for the info!