If working from outside the US for x days, will one fill one's US taxes as if one stayed the entire year in the US?

Question

Assume a US citizen or a US lawful permanent resident is domiciled in California. Their employer's headquarters are based on California, and their work office is in California. If they go outside the US and work from outside the US for x days, will they fill their US taxes as if they stayed the entire year in the US? Assume that they aren't filling the US tax forms avoid double taxation and that the US lawful permanent resident isn't endangered by the stay outside the US.

Answer 1

US citizens and resident aliens enter their worldwide income on their tax form (1040). It doesn't matter where the source of the income is.