Calculators can be a bit of information but I also find them really lacking in some of the critical points. So that leaves me going about the stocking question a bit more in depth.
Before adding more fish, think of how the tank is running with the current set,
One of the major points I feel computers miss is the human factor! How busy and how interested you are in the job is a major deciding factor on stocking. How much time does life leave you for fish and how much energy do you want to expend to keep it running well? Those are just as important as how many of what.
Do you currently keep the water changed to keep pollutants like nitrate well down? Are you able to keep the filters running well enough to do their job? If the answers are a solid "yes", I would feel you have room for more. If you are just getting by and about to hit a spot in life where far more time is needed away from the tank, I go with a solid "NO".
You will know far more about this than the computer!
For choices, there are hundreds but for my pleasure, I like a largish single fish with real interest over small dither type fish.
But then you will know far more about that angle than I would!!