Of course it’s on the total but if you don’t owe anything at the end of the year it doesn’t apply, only if you owe.
I’m sorry, sir... but you are wrong.
Let’s say you made $50,000 last year and your state income tax liability was $2,000.
Over the course of the year your employer withheld $1,900 from your paycheck for California State Income tax withholding - and you owe $100 when you file your taxes.
The surcharge would be 5% of $2,000 ($100), NOT 5% of $100 ($5)