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My annual income in the US would be $60000.
I understand this is taxable at 30% amounting to $3500 per month(is this correct?).
If I have 2 dependants on H4(my spouse and baby), what would be the tax rebate? How much more money would I end up in hand per month?

For income tax, it is NOT a flat 30%. It progesses up from 0%, then 10%, then 15%, then 25%.

Social Security (6.2%) and Medicare (1.45%) are flat taxes.

If you factor in state income taxes, then the final result MAY be 30%.

Doing a tax return for you requires time and effort on my part, something I have in short supply this time of year. If you want to pay me to calculate your tax liability, see my email address below.