Form 1120-S is the tax return for an S corporation, atype of elected business structure. It reports the corporation’s income, losses, deductions, and credits. S corporations themselves generally don’t pay federal income tax. On the other hand, Form 1040 is the standard tax return for individuals, including US expats. It reports your personal income, deductions, and credits from various sources, including your share of income (or loss) from an S corporation.