May Tax Deadlines for US Small Business in 2026
All important May 2026 tax deadlines for sole proprietors, LLCs, S-Corps, and C-Corps. Don't miss a filing.
April 24, 2026 1 min readby TinSuite Team
tax deadlines may calendar
Tax deadlines are easy to miss — and expensive. Here's every major federal tax deadline in May 2026 that affects US small businesses.
Quick overview
- May 15 — Tax-exempt org (Form 990) deadline
- May 31 — Mid-year sales tax compliance review (recommended)
Detail on each deadline
May 15: Tax-exempt org (Form 990) deadline
Missing this deadline usually triggers a penalty of 5% per month (capped at 25%) plus interest. File even if you can't pay — the failure-to-file penalty is 10x the failure-to-pay penalty.
May 31: Mid-year sales tax compliance review (recommended)
Missing this deadline usually triggers a penalty of 5% per month (capped at 25%) plus interest. File even if you can't pay — the failure-to-file penalty is 10x the failure-to-pay penalty.
Not sure which deadlines apply to you?
It depends on your entity type:
- Sole proprietor / single-member LLC: file Schedule C with Form 1040 by April 15
- Multi-member LLC / partnership: Form 1065 by March 15
- S-Corp: Form 1120-S by March 15
- C-Corp: Form 1120 by April 15 (or 15th of 4th month after fiscal year-end)
- Employer: Form 941 quarterly, W-2/1099 annually
How TinSuite helps you stay on top
- Deadline calendar built into your dashboard
- Email and in-app reminders 7 and 1 day before each deadline
- Pre-filled forms generated from your books — just review and file
- Multi-state aware — adds state deadlines based on your nexus