There are two different things involved here -- (a) exemption from counting days present -- this is generally for five calendar years counting the year of first admittance-- for F-1 visa holders; (b) FICA withholding -- generally all foreign and some domestic students are exempt from having to have FICA withheld -- the logic here is that as a non-resident alien and with no intention of staying in the USA past the study period, it makes no sense to pay in towards FICA ( you will never be eligible to collect). For US students during residency/ training it is viewed as "not employment" and therefore no FICA.
F-1 students , even on extended F-1 ( unless gainfully employed ) i.e. not on OPT etc. there is NO FICA. If you however, are not compliant with F-1 and/or changed to H-1B, then this employment earnings and therefore subject to FICA.
8843 is generally the form used to declare that a a person is still a non-resident alien, closer connection to home country, has no intention of staying in the USA and therefore not subject to FICA
Namaste ji
