You do not have to pay income tax if you spend less than 30 days in the US that calendar year.
Careful with tax advice from the Internet, folks. idlewords is talking about passing the Physical Presence Test for the Foreign Earned Income Exemption. If you quality for the FEIE via either the physical presence test or the bona-fide residence test (see the IRS docs, they are fairly easy to understand), you get to exempt the first X of your income from the income tax. X is in the $80k range this year, check your friendly local IRS website.
Regardless of the FEIE, your income is not exempt from self-employment taxes, as idlewords said. Additionally, it has to be EARNED income, a distinction which has VERY IMPORTANT CONSEQUENCES for people here who are intending to sell their startup at some point. To oversimplify, earned income is the portion of your profit you gain in return for services rendered, but it excludes the return on invested capital -- including IP. So if you end up selling your business for $500,000, it is highly likely that large portions of that are not earned income, and will be taxed from the first dollar in the US.
Taxes are a minor headache for me every year, and this year my business gets to start filing with Japan, too. Yaaaaaay, more fun.
Careful with tax advice from the Internet, folks. idlewords is talking about passing the Physical Presence Test for the Foreign Earned Income Exemption. If you quality for the FEIE via either the physical presence test or the bona-fide residence test (see the IRS docs, they are fairly easy to understand), you get to exempt the first X of your income from the income tax. X is in the $80k range this year, check your friendly local IRS website.
Regardless of the FEIE, your income is not exempt from self-employment taxes, as idlewords said. Additionally, it has to be EARNED income, a distinction which has VERY IMPORTANT CONSEQUENCES for people here who are intending to sell their startup at some point. To oversimplify, earned income is the portion of your profit you gain in return for services rendered, but it excludes the return on invested capital -- including IP. So if you end up selling your business for $500,000, it is highly likely that large portions of that are not earned income, and will be taxed from the first dollar in the US.
Taxes are a minor headache for me every year, and this year my business gets to start filing with Japan, too. Yaaaaaay, more fun.