Our readers asked us to cover the topic on filing U.S. federal income tax return if you are a U.S. citizen living in the UK. The starting point for any US expat tax-related topic is gaining a clear understanding who needs to file US taxes on their worldwide income: U.S. persons. Who is required to file a tax return by U.S. tax law? Individuals, who are U.S. citizens, including the ones with dual citizenship (U.K./U.S. in this case), also Green Card holders abroad. Everyone who earns a minimum required threshold has to file a tax return and pay taxes they may owe. Below are numbers for the 2017 year tax return to file in 2018: If you are under age 65 and single, your minimum income requirement is $10,400 If you are 65 or older, then filing requirements raise slightly to $11,950 For self-employed individuals, the threshold is $400 regardless of age and filing status.