Accounting period
What it is
The span of time covered by a set of company accounts — usually 12 months. It runs to the company's accounting reference date (ARD), which is the company's year end. HMRC uses the accounting period to set Corporation Tax deadlines.
Why it matters
Your accounting period sets three key deadlines: annual accounts due 9 months after the end; Corporation Tax payment due 9 months and 1 day after; CT600 return due 12 months after. All three are different — and all three carry penalties if missed.
Common mistake
Assuming the accounting period always runs January to December. It ends on whatever date was set as the accounting reference date — often the last day of the month of incorporation.
Official source
GOV.UK — Accounting periods for Corporation Tax ↗Disclaimer
General educational guidance only — not legal, tax, accounting, immigration, investment or financial advice. We don't guarantee the information is complete, current or suitable for your situation. Always check official sources (GOV.UK, Companies House, HMRC, the relevant professional body) and speak to a qualified professional before acting. Last reviewed: June 2026.