I know how the US tax system works.
First of all US Persons are granted either a standard deduction or itemized deductions. The standard deduction is currently US$ 24,800 (S$ 34,500). Most people itemize deductions for medical, education expenses among others when such deductions are higher than the standard deduction. Getting into deductions is a lengthy discussion.
For any outstation US people they can exclude foreign earned income exclusion of US$107,600 (S$150,000) plus a housing exclusion of US$ 31,770 (S$45,000) If married the exclusion doubles to US$ 215,000 (S$300,000) so you are looking at S$ 345,000 for a married couple. Adding the above S$ 34,500 standard deduction you arrive at S$379,000 before any tax liability accrues.
Most people itemize deductions and if the US person has children, they can claim the child tax credit of US$ 2,000 per child. A Tax credit is different than tax deduction because its a direct offset of tax liability. Furthermore, if the US person has no tax liability and has children, the IRS will pay the US Person US$ 1400 per child, as a refund.
The US tax system is complicated, but the actual rates of taxation is fair after everything is tabulated. The paperwork is a nightmare.