CT600 Filing Deadline Calculator: When Is Your Return Due?

CT600 Filing Deadline Calculator: When Is Your Return Due?

Your CT600 filing deadline and Corporation Tax payment deadline are different dates. Here's how to work out yours.

The Two Deadlines

You should pay before filing — the payment deadline comes first.

Quick Calculator

How to Calculate Your Deadline

Filing Deadline

12 months after your accounting period ends.

Period ends 31 March 2025 → File by 31 March 2026.

Payment Deadline

9 months and 1 day after your accounting period ends.

Period ends 31 March 2025 → Pay by 1 January 2026.

First Period (New Companies)

Your first accounting period starts on your incorporation date. Your first year-end defaults to the anniversary of the month-end after incorporation.

Example: Incorporated 15 June 2025 → First year-end 30 June 2026.

But you can change your year-end (once) to make it more convenient — many companies choose 31 March to align with the tax year.

Short Accounting Periods

If your accounting period is shorter than 12 months (e.g., first period or changing year-end), the deadlines are calculated from the period end date, not a full 12 months.

Example: Period 1 July 2025 to 31 December 2025 (6 months)

• Payment due: 1 October 2026
• Filing due: 31 December 2026

What If the Deadline Falls on a Weekend?

If the filing deadline falls on a weekend or bank holiday, the deadline is the next working day.

HMRC Free Filing Service Closing

⚠️ Important: HMRC's free CT600 filing service closes 31 March 2026. After that date, you'll need commercial software to file.

Taxpipe is £59 per filing — no subscription, no hidden fees.

Don't miss your deadline. File your CT600 with Taxpipe today.

Related Reading

• How to Use HMRC Government Gateway to File Your CT600
• CT600 Nil Return: How to File When Your Company Has No Trading Activity
• Company Formation & Corporation Tax Registration