If you moved out of the US in August 2018, you need to either file a
full year US resident tax return declaring your worldwide income for
calendar year 2018 (and claiming foreign tax credit to help offset any
foreign income earned from August to December 2018) or you will have to
file a Dual Status return (part year resident and part year
nonresident).
Dual Status returns are a bit complicated and
you are not allowed the standard deduction and must file married filing
separately. Please see Publication 519 page 32 https://www.irs.gov/pub/irs-pdf/p519.pdf
If you file a dual status return, you will be able to take an exemption for the months you were not in the US.
If
you file a full year resident return, you can qualify under the
physical presence test where you are overseas for 330 days in any 12
month period.
You can claim the coverage exemption for any month during your tax year that’s included in the 12-month period.
