读者 Jenny 持H1-B签证来美国高校做博士后，听说自己是「非居民」不用交联邦税和州税，又听说「H1B前3年免联邦税和州税」。这是误解。她的情况前3年不用交联邦税，原因是中美之间对此有税务协议，和 RA/NRA 以及H1B没有关系。
(Teachers, Professors and Researchers)
An individual who is, or immediately before visiting a Contracting State was, a resident of the other Contracting State and is temporarily present in the first-mentioned Contracting State for the primary purpose of teaching, giving lectures or conducting research at a university, college, school or other accredited educational institution or scientific research institution in the first mentioned Contracting State shall be exempt from tax in the first mentioned Contracting State for a period not exceeding three years in the aggregate in respect of remuneration for such teaching, lectures or research.
访问学者一般是 J-1 身份，也有少数的 H-1B，如上面这位读者。关于在美国有工资收入的博士和博士后如何报税，参见这篇文章。
「Three years in the aggregate」 如何计算
既然是「aggregate」，所以无需是连续的3年，若中途离开美国、回到中国、之后再次回来美国，仍然可以接着计算。参见 IRS 在这份文件里举的例子：Thus, for example, a resident of China who visits the United States to conduct research at the National Institute of Health (NIH) for two years, 1986 and 1987, returns to China for a year, and then comes back for another year of research at NIH in 1989 would be exempt from tax on his NIH remuneration for each of the three years. However, if he stayed at NIH in 1990 or returned at a later time the exemption would no longer be available。
「年」的计算是从抵达美国之日起计算365天。最接近官方解释的是IRS 2014 年的一份备忘录，里面引用了 US-UK Tax Treaty 的先例，并举了一个例子，是这样计算的：
It is the purpose of [the exemption under Article 18 of the 1945 U.K. treaty] that such exemption shall cease at the end of 2 years from the date of [the individual’s] initial arrival in the United States. Thus, if [the individual] reaches the United States on July 1, 1945, he is exempt with respect to his remuneration earned in the United States up to June 30, 1947.
上面提到的 2014 年备忘录，是关于中美 Treaty Article 19 是否适用于在美国留学之后留下来教学的人员，其意见认为，只要满足以下4个条件即可使用 Article 19：
- the individual is a resident of China for the year at issue or was a resident of China immediately before visiting the United States as a student or trainee;
- the individual is 「temporarily present」 (notwithstanding the fact that the individual was present in the United States in prior years solely for educational or training purposes) in the United
States for the year at issue for the primary purpose of teaching, giving lectures, or conducting research;
- the individual's teaching, lecturing, or research activities take place at a university, college, school, or other accredited educational institution or scientific research institution in the United States; and
- the individual has not claimed benefits under Article 19 for more than three years in the aggregate.
只要满足上述条件（只是临时职位、之前没用过或没用完 Article 19），即使是留学毕业之后立刻留在美国教书，仍然可以使用 Article 19 免税。若以前已经用完了 Article 19 的36个月免税条款，今后就不能再用了；比如说：你 2000/07/01-2003/06/30 用 Article 19 享受了3年的免税期，回中国工作了几年，2006年再次来美国从事科研教学工作，就不能再享受3年的免税了。
(Students and Trainees)
A student, business apprentice or trainee who is, or was immediately before visiting a Contracting State, a resident of the other Contracting State and who is present in the first- mentioned Contracting State solely for the purpose of his education, training or obtaining special technical experience shall be exempt from tax in that Contracting State with respect to:
- payments received from abroad for the purpose of his maintenance, education, study, research or training;
- grants or awards from a government, scientific, educational or other tax-exempt organization; and
- income from personal services performed in that Contracting State in an amount not in excess of 5,000 United States dollars or its equivalent in Chinese yuan for any taxable year.
The benefits provided under this Article shall extend only for such period of time as is reasonably necessary to complete the education or training.
中国居民来美国学习或接受培训，学费、奖学金等收入无需交税；其他个人收入享有5,000美元的免税额度。这里的 taxable year 是指 calendar year，而不是365天。留学生一般是 F-1 或 M-1 签证。
本站一位作者以F-2身份入境美国，后来转成F-1读书，用学校提供的软件报税时发现无法 claim 这一条 treaty。根据读者 Andy F 的查找，IRS 在2002年对此的解释如下：
Individuals who first enter the U.S. as an F-2 or H-4 are NOT eligible to claim the tax treaty benefit for students as they did not enter the U.S. for the purpose of being a student. The Treasury Dept is very specific about China in particular.
In general, persons who change immigration status from dependent to principal are not eligible for tax treaty benefits UNLESS the change to principal occurs within two months from the original arrival in the U.S. The IRS maintains that it is the PURPOSE for original arrival in the U.S. that determines treaty eligibility. Therefore, if someone changes purposes (goes from dependent to student, for example) they cannot benefit from tax treaty exemptions. AND, in the case of an F-2 who has been in the U.S. for a year or so, passes the TOEFL and goes home for the summer to apply for an F-1 visa and returns that fall, the IRS still says a resounding no to treaty benefits. This is because the NRA hasn't been physically residing in the treaty country for at least a year prior to their arrival as a student in the U.S. Officially, they're from "no country" for tax purposes, because they're an NRA in the U.S., but U.S. tax law also has them as a nonresident in the home country. (There are a few exceptions to this, but mostly for diplomats who are considered tax residents of their home country no matter where they live or how long they've been away from home.)
IRS 认为，他们使用其他签证入境，其目的不是来求学，因此不能享受此 treaty。