how is tax formulated on monthly wages?

Answer 1

ssn is about 7.5% of gross wages,
fed is about the same
state is whatever the state is

and if you wish, and you have a good place to put it, you can legally be deferred from fed income taxes and thus, have none of THOSE type
taken from your pay. ASK A CPA about that.

Answer 2

UK answer: The tax free allowances contained in the employee's PAYE code number are divided by 12 and one twelfth is deducted from the monthly salary. The remaining pay is taxed as to one twelfth of the 10% band, one twelfth of the 22% band and, if applicable, the balance at 40%.
The resulting tax due is added to the tax due so far in the year, the tax paid so far in the year is deducted from this and the result is the tax due this month. This means that if pay varies from month to month, you always pay the correct tax.
A very elegant system which has been around since the War and never failed us.
Sadly, it relies on human beings to operate it and to remember not to lose their P45 when moving from one job to another.
I don't really miss it much.

Answer 3

your employeer has a table that tells them how much to withhold. It doesn't work so good for people that get paid a lot one month and nothing the next month or a lot and a little.