As from the Smite Wiki
Your Base Damage is Calculated as:
Base Damage + (Base Damage per lvl × God's lvl) + (100% of Physical Power OR 20% of Magical Power)
Then comes the Defence:
Damage = (100 × Unmitigated Damage)/(Protections + 100)
And the Penetration and Reduction:
Actual Defense = (Protection × (1-%Reduction) - Flat Reduction) × (1-%Pen) - Flat Pen
Where
- Percent Reduction. This will reduce a target's protection values by a percentage. For example, The Executioner will reduce a target's physical protection by 7% (per stack).
- Flat Reduction.. This will reduce a target's protection values by a specific amount. For example, Void Stone will reduce a target's magical protection by 15.
- Percent Penetration. This will reduce a target's protection values by a percentage. For example, Obsidian Shard will reduce a target's magical protection by 33%.
- Flat Penetration. This will reduce a target's protection values by a specific amount. For example, Warrior Tabi will reduce a target's physical protection by 15.
And to Answer your Question: There is no difference from magical and physical and there is no "simple" way :P