What CT600F is for

CT600F is the HMRC supplementary page for tonnage tax. HMRC guidance says to complete CT600F if the company operates ships and is a party to a tonnage tax election.

The page is specialist because it is not only a box indicator. It links the company or group election, ship operation, qualifying shipping activities, offshore training allowance, relevant shipping profits, and the tonnage tax profit amount that feeds the main CT600.

When CT600F may be needed

Start with the shipping activity and election status. CT600F is not for every company with marine income; it is for cases where the tonnage tax regime applies and the supplementary details need to accompany the Company Tax Return.

The company operates ships.
The company is party to a tonnage tax election or a tonnage tax group election.
Relevant shipping profits need to be reported in the CT600 package.
Chartering-in limits, training commitment, offshore activity, or qualifying ship detail needs review.
The CT600 supplementary-page indicator needs to agree with the return being filed.

When CT600F is usually not the right page

A useful review also records why CT600F was not included. Marine services, port services, freight agency work, or income connected with ships does not automatically mean the company is inside tonnage tax. If there is no tonnage tax election, the filing team should normally keep the shipping analysis in the Corporation Tax computation rather than turning on CT600F.

Borderline cases deserve an explicit review note because the filing error can go both ways: omitting a required CT600F can leave the return incomplete, while including CT600F without an election can create questions the computation does not support.

What information belongs in the CT600F review

A strong CT600F workflow should make the election facts, group position, ship data, and main-return effect visible before filing. That matters because the supplementary page drives values in the main CT600 as well as supporting the specialist regime.

Company name, tax reference, and accounting period.
Whether the company was party to a tonnage tax group election.
The name of the tonnage tax group where relevant.
Training commitment and chartering-in limit answers.
Offshore activity and offshore training allowance detail where relevant.
Relevant shipping profits and tonnage tax profit calculations.
Ship-level days, tonnage, and qualifying activity support.

Main CT600 consequences to check

The reviewer should trace the CT600F figures back into the main return before filing. In practice, the key question is whether the tonnage tax profit figure used in the Corporation Tax computation agrees with the supplementary page and whether the supplementary-page indicator is switched on only when the filed package contains CT600F.

Does the tonnage tax profit amount reconcile to the main CT600 computation?
Does the CT600F indicator match the supplementary page actually being submitted?
Are non-tonnage shipping profits kept separate from tonnage tax profits?
Has the group election position been reviewed where the company belongs to a tonnage tax group?

Common CT600F workflow traps

The first trap is treating CT600F as a specialist appendix after the CT600 has already been reviewed. The tonnage tax profit amount can affect the main CT600, so the supplementary page should be checked before sign-off.

The second trap is losing sight of the group position. HMRC's guidance expects the group election and group details to be handled deliberately where the company is part of a tonnage tax group. The third is stale process around flagging rules: for return periods starting on or after 1 April 2022, HMRC guidance says the old flagging boxes should not be completed in the same way.

Example review scenarios

A standalone ship operator with a live tonnage tax election usually needs the CT600F indicator, election details, ship data, and tonnage profit trace reviewed together. A group case needs the same review plus the group election identity and any group-level facts that support the return.

By contrast, a company earning incidental income from marine customers may have a Corporation Tax issue without a CT600F filing requirement. The working paper should explain the conclusion so the reviewer does not infer that a missing CT600F page is an oversight.

How Robocount handles CT600F workflow

Robocount keeps CT600F in the same Corporation Tax review workflow as the main CT600, so specialist shipping data can be checked before the filing package is submitted.

Tracks the CT600F supplementary-page indicator and filing output.
Captures election, group, training, chartering, and offshore review points.
Keeps tonnage tax profit data visible alongside the main CT600 calculation.
Supports a review trail for specialist shipping assumptions.
Helps practices avoid burying tonnage tax in free-text working papers.

Evidence trail to keep with the return

Tonnage tax election or group election evidence.
Ship lists, days, tonnage, and qualifying activity support.
Training commitment and chartering-in limit review notes.
Bridge from relevant shipping profits to the CT600 computation.
Reviewer sign-off on any offshore training allowance treatment.

Review checklist before filing

Confirm the company operates ships and is within a tonnage tax election.
Check whether the case is a standalone company or group election case.
Review training commitment, chartering-in limit, and offshore activity answers.
Trace tonnage tax profits to the main CT600 amount.
Document why CT600F is included, or why a shipping-related case does not need it.
Keep the ship-level and election evidence with the Corporation Tax working papers.

FAQ

Is CT600F needed for every shipping company?

No. HMRC's CT600F guidance is for companies that operate ships and are party to a tonnage tax election. Other shipping or marine activity may need Corporation Tax analysis without CT600F.

Does CT600F affect the main CT600?

Yes. CT600F includes tonnage tax profit information that should agree with the relevant main CT600 boxes and the company's Corporation Tax computation.

Why does CT600F matter for accounting practices?

Tonnage tax cases are rare for many practices, but they are high consequence when they arise. A structured review reduces the risk of missing election, group, shipping-profit, or supporting-evidence points.

Useful HMRC references

This guide is general product and filing workflow information, not tax advice. Check the current HMRC guidance and the company's shipping and election facts before filing.

CT600F: tonnage tax elections, shipping profits, and specialist review points.