Naturally carbonating keg question

Have any of you used Beersmith's calculations for the amount of priming sugar to use for naturally carbonating in a keg to a particular volume of CO2? Anyone know if it gets reasonably close?

I have a tripel that I want to age for a couple of months before I put it on tap, so I figure I might as well get it carbonating while I wait, but I've never tried naturally carbonating in a keg before.

It works well. Set the temp correctly for when you add the priming sugar and it gives a good approximation.