Form 1120-S Checklist for Accountants: S Corp Tax Return Workflow (2027)

S corporation returns arrive early in tax season, with the same March deadline as partnerships. Firms that start them in mid-February end up filing extensions they didn’t plan for. This 1120-S checklist gives you one process to run for every S-corp client, from the organizer to the K-1s.

Below you’ll find the 2027 dates, the 11-step Form 1120-S workflow, and a free template you can load into Jetpack Workflow for every S-corp client.

Key Form 1120-S dates for calendar-year S corporations

An extension extends the time to file, not to pay. Shareholders still need their K-1s to file their own returns, so late S-corp returns delay your individual clients too.

The Form 1120-S checklist (step by step)

1. Send the engagement letter and information request. Send it in January with an organizer listing what you need: year-end financials, shareholder changes, distributions, fixed asset additions and officer compensation.
2. Receive the signed engagement letter and client information, and confirm Form 2553 is on file. Confirm the S election is in place for the year. A missing or late election changes how the entity files.
3. File an extension if information won’t be ready by March 15. Decide by early March. Filing Form 7004 on time avoids the late-filing penalty, which is charged per shareholder for each month the return is late.
4. Prepare the return. Tie the return to the year-end books, and review reasonable compensation, distributions and shareholder basis.
5. Review the return and clear review notes. A second person reviews before anything goes to the client.
6. Send the return to the client for review with Form 8879-S. Form 8879-S is the signature authorization that lets you e-file on the corporation’s behalf.
7. Receive the signed Form 8879-S. Don’t e-file until it’s back.
8. E-file the return and confirm acceptance. Save the acceptance to the client file.
9. Distribute K-1s to shareholders. Shareholders need them for their individual returns, so send them as soon as the return is accepted.
10. Deliver the final return and save it to the client file.
11. Send the invoice and confirm payment. Billing is part of the checklist, so it isn’t forgotten after a long March.

Common Form 1120-S mistakes

• No election on file. Step 2 confirms Form 2553 before work begins.
• Deciding on extensions too late. Step 3 has its own due date in early March.
• Filing before the 8879-S is signed. Steps 6 and 7 make the signature a required task.
• K-1s sent late. Step 9 sends them the day the return is accepted, so individual returns aren’t held up.

How to run 1120-S returns for every client at once

March is the busiest month for business returns, and S-corp and partnership returns share the March 15 deadline. In Jetpack Workflow, you apply the 1120-S template to every S-corp client, and the Form 1065 template to partnerships, with due dates calculated from March 15. Everyone on your team can see which returns are waiting on the client, which are in review and which still need an 8879-S signature.

FAQ

When is Form 1120-S due in 2027?

For calendar-year S corporations, Form 1120-S for tax year 2026 is due Monday, March 15, 2027. With a Form 7004 extension, the deadline moves to September 15, 2027.

What is Form 8879-S?

Form 8879-S is the IRS e-file signature authorization for Form 1120-S. The corporate officer signs it so the preparer can e-file the return.

What is Form 2553?

Form 2553 is the election a corporation files to be taxed as an S corporation. Confirm it’s on file before preparing an 1120-S.