Individuals: If you are not paying your 2019 income tax through withholding (or will not pay enough tax during the year that way), pay the second installment of your 2019 estimated tax.
If you are a U.S. citizen or resident alien living and working (or on military duty) outside the United States and Puerto Rico, file IRS Form 1040 and pay any tax, interest, and penalties due for 2018. If you want additional time to file your return, file IRS Form 4868 to obtain four additional months to file. Then, file IRS Form 1040 by October 15.
Corporations: Deposit the second installment of estimated tax for 2019.
Employers: For Social Security, Medicare, withheld income tax, and non-payroll withholding, deposit the tax for payments in May if the monthly rule applies.