Amending a CT600 or Accounts Filed Outside TinyTax

Clear Books Tax can only amend CT600s and Companies House accounts that were originally filed through Clear Books Tax. If your original submission was made via HMRC's online services, Companies House WebFiling, or any other platform, the amendment must be made through that same route.

Why This Limitation Exists

Clear Books Tax's amendment feature works by creating a revised version of your original submission using the filing record stored in Clear Books Tax. If the original was filed elsewhere, there is no Clear Books Tax record to amend from — and Clear Books Tax cannot access submissions made through other platforms.

How to Amend a CT600 Filed via Gov.UK or HMRC Online Services

1. Log in to your company's HMRC online account at gov.uk
2. Navigate to your corporation tax return for the relevant period
3. Choose to file an amended return and submit your corrected figures

Deadline: You must submit your amendment within 12 months of your original filing deadline (not the period end). For example, if your filing deadline was 31 October 2025, the amendment deadline is 31 October 2026.

How to Amend Accounts Filed via Companies House WebFiling

1. Log in to Companies House WebFiling (ewf.companieshouse.gov.uk)
2. Select the option to file revised accounts for the relevant period
3. Complete and submit the amended accounts

Using Clear Books Tax for Future Filings

If you would like to use Clear Books Tax for future periods, you can add your company at any time. Once a period is filed through Clear Books Tax, all subsequent amendments for that period can be handled directly from your dashboard.

Common Questions

Can I file an amended CT600 through TinyTax even if the original was filed elsewhere?

No — the Amend feature requires the original CT600 to already be in the Clear Books Tax system. For returns filed via HMRC online services or another platform, the amendment must go through that same route.

What if I want to switch to TinyTax from my next accounting period?

You can add your company to Clear Books Tax at any time and file your next period through us. Just enter your company number on the Clear Books Tax homepage to get started.