CT600 supplementary pages

Supported HMRC supplementary pages for CT600 returns.

Robocount treats supplementary pages as part of the Corporation Tax engine. Each supported page is connected to the CT600 workflow, computation logic, review trail, and HMRC filing output.

CT600A loans to participators

Close company loans, s455 tax, repayments, releases, and relief tracking.

Indicator box 95

CT600B controlled foreign companies

CFC charge data, hybrid mismatch indicators, and related Corporation Tax disclosures.

Indicator box 100

CT600C group relief

Group relief claims, surrendered losses, carried-forward claims, and consent detail.

Indicator box 105

CT600D insurance companies

Insurance companies, friendly societies, Overseas Life Assurance Business, and OLAB review points.

Indicator box 110

CT600E charities and CASCs

Charity and CASC exemption claims, qualifying-purpose review, and repayment detail.

Indicator box 115

CT600F tonnage tax

Tonnage tax elections, group cases, shipping profits, offshore training allowance, and CT600 review points.

Indicator box 120

CT600G Northern Ireland

Northern Ireland indicators, trading-activity review, rest-of-UK split checks, and evidence trail.

Indicator box 125

CT600H cross-border royalties

Cross-border royalty payments, reasonable-belief treaty relief, withholding, and recipient detail.

Indicator box 130

CT600I ring fence trades

Ring fence trade profits, financing-cost adjustments, allowances, and supplementary charge payable.

Indicator box 135

CT600J tax avoidance schemes

DOTAS scheme references, promoter reference numbers, expected tax advantage periods, and disclosure review.

Indicator box 140

CT600K restitution tax

Restitution interest, specialist tax-charge review, double-count checks, and CT600 reconciliation.

Specialist tax cases

CT600L R&D relief

RDEC, SME/ERIS style credit details, payable credit steps, and R&D claim support.

R&D credit detail

CT600M freeports and investment zones

Tax-site evidence, enhanced allowances, capital allowances review, and qualifying-activity checks.

Freeport and investment zone cases

CT600N RPDT

Residential Property Developer Tax, adjusted development profit, allowance, and RPDT payable.

RPDT cases

CT600P creative industries

Creative industry relief, AVEC/VGEC, production-level detail, and payable credit cascade support.

Creative industries

HMRC Company Tax Return service closed

What changed after 31 March 2026, why commercial software is now needed, and how CT600 filing works.

Filing route change

Corporation Tax payment deadlines

Payment timing, CT600 filing dates, late interest, payment evidence, and audit-trail controls.

Deadline workflow

Dormant company and nil CT600

When a dormant or nil-tax company still needs HMRC review, CT600 filing, or Companies House separation.

Dormant and nil cases

Marginal Relief CT600 software

Small profits rate edge cases, associated-company checks, threshold review, and CT600 computation workflow.

Rate calculation

Directors' loan repayment timing

CT600A timing, section 455 tax, relief claims, L2P, and repayment review workflow.

CT600A follow-up

Corporation Tax losses

Trading losses, current-year relief, carry-back claims, carried-forward schedules, and CT600 evidence.

Loss workflow

Capital allowances in CT600 software

AIA, full expensing, writing down allowances, disposals, pools, and computation review.

Computation workflow

CT600 client approval workflow

Manager review, client sign-off, iXBRL attachments, supplementary-page checks, and filing approval evidence.

Practice approval

Owner-managed company CT600 evidence pack

Director loans, dividends, payroll, allowances, losses, approval, and payment records for practice files.

Small-company evidence

CT600 payment reconciliation workflow

Payment references, nil-to-pay cases, refunds, interest, evidence, and post-filing client follow-up.

Post-filing control

CT600 filing deadlines and penalties

Return deadlines, payment dates, late filing penalties, determinations, and practice deadline controls.

Deadline control

Corporation Tax repayment claims

Overpayments, loss carry-back claims, repayment interest, amendments, and CT600 evidence workflow.

Repayment workflow

iXBRL accounts and computations

Attachment checks, accounts and computation alignment, online filing obligations, and API-ready return packages.

Attachment workflow

Associated companies and Marginal Relief

Threshold reductions, short periods, augmented profits, and small-company Corporation Tax rate review.

Rate review

R&D additional information workflow

Claim notification, additional information, CT600 boxes 656 and 657, CT600L, and approval evidence.

R&D controls

Final-period CT600 before dissolution

Final accounts, company closure, strike off, stub periods, HMRC filing evidence, and payment checks.

Closure workflow

Creative industries CT600P evidence workflow

AVEC, VGEC, additional information, project evidence, payable-credit checks, and filing approval workflow.

Creative claims

Government Gateway CT600 rejection troubleshooting

Validation errors, authorisation checks, iXBRL attachment issues, supplementary-page mismatches, and resubmission evidence.

Rejected returns

Corporation Tax repayments workflow

Repayment claims, overpayments, client communication, HMRC evidence, and bank-detail controls.

Repayment control

CT600 iXBRL version control

Amended returns, iXBRL accounts, computations, approval packs, and submission evidence.

iXBRL control

CT600 amendment window

The 12-month amendment window, overpayment relief, underpaid tax disclosure, revised attachments, and client approval.

Post-filing correction

Group relief evidence workflow

Claimant and surrendering company checks, consent notices, carried-forward group relief, and replacement claims.

CT600C evidence

Agent authorisation and Gateway setup

Corporation Tax agent authority, Government Gateway setup, client credential boundaries, and submission evidence.

Filing access

CT600 final period workflow

Company closure, cessation, final accounts, strike-off evidence, payment control, and HMRC filing review.

Closure workflow

Associated-company threshold evidence

Associated-company counts, Marginal Relief thresholds, short periods, client declarations, and CT600 review notes.

Threshold evidence

CT600A section 455 repayment timing

Close company loan relief, CT600A claims, L2P timing, repayment evidence, and client expectation control.

Section 455 relief

CT600C consent evidence

Claimant and surrendering company checks, consent notices, carried-forward group relief, and replacement-claim audit trail.

Group relief control

CT600P payable credit review

Creative industry credit review, set-off checks, additional information, group surrender, and filing approval evidence.

Creative payable credits

CT600 payment reference reconciliation

Accounting-period payment references, nil-to-pay cases, overpayments, refund details, and privacy-safe client communication.

Payment control