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You can use the Layout XL tool for area estimation.
In your schematic window, you can go to Tools->Design Synthesis->Layout XL. It will open a layout editor window. From there, you can go to Design->Generate from source. In this form, on the bottom left, you'll have the area utilization option where you can fill the percentage of the total area. This depends on the routing line widths, and matching constraints.
The general rule is that for low power analog circuits, you can use an area of around 65%~75%. for high power circuits, it can go down to 55-60%.
For custom digital circuits, it can be 80-85%.
Again, these will only give you quick rough estimates.
Nothing like doing a detailed floor plan.