MarvinSketch can calculate some basic properties for your structures, which can be pasted into your drawing.
The calculations update upon modification except if they applied to a selection. For more information see Analysis Box
You can set the properties you want to be displayed and their order as well.
Formula with charge
Dot-disconected formula with charge
The decimals setting applies to the exact mass value only.
By default the value of molecular weight is set to three decimal places.