Depends what you mean by calculation of CG.
If you mean continuously calculating an assumed CG based on zero fuel weight data and fuelk tabnk quantities (or on landing gear loads at startup, say, and then subtracting fuel burn) then I'm sure there are FMSs doing variants of those.
But those aren't really calculating CG - they are estimating it. There's always going to be some margin of error due to the inherent inaccuracy of the input data - especially fuel quantities within tanks.
The alternative is to calculate CG based on aerodynamic behaviour - that's a LOT harder. The problem is that unless you have near-perfect knowledge of the aircraft aerodynamic characteristics then you'll end up needing to know the cg in order to work out the CG - the equations of trim end up cancelling each other out. The only way to break the cuircle is to measure a load directly - like tailplane strain gauging would - but that brings its own problems. If you just go for a "compare the stab-to-trim to prediction" method your accuracy won't be much better than the predictive FMS style system.