Corporation Tax & CT600

CT600 software that files corporation tax to HMRC

AccLedger prepares the full CT600 from your bookkeeping — adjusting for depreciation, capital allowances, R&D relief, marginal relief, s455 close-company loan tax and trading losses — and submits the iXBRL return to HMRC. Made for UK limited companies and the accountants who serve them.

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HMRC-recognised · 90-day free trial · From £10/month

Profit-to-tax bridge, automated

AccLedger pulls your accounting profit, adds back depreciation and disallowables, deducts capital allowances, applies trading losses, and arrives at taxable profit — with every adjustment visible and editable.

Capital allowances done right

AIA (Annual Investment Allowance), main pool WDA, special rate pool, and FYA — all calculated per asset, with the pool brought forward, additions captured and disposals netted off.

Marginal relief for the £50k–£250k band

Companies with profits between the small-profit and main rate thresholds get marginal relief calculated automatically, with associated companies factored in.

s455 close company loan tax

Loans outstanding to directors or participators at the year end attract s455 tax at 33.75%. AccLedger calculates it from your director loan balance and posts it to Box 505 of the CT600.

R&D relief and CT600L

Claim R&D enhanced deduction or RDEC where applicable. AccLedger surfaces the deduction in your CT600 calculation and prompts you to attach the supporting CT600L supplementary.

iXBRL submission to HMRC

AccLedger generates the iXBRL-tagged accounts and computations alongside the CT600 form, and submits the full package to HMRC through the recognised CT endpoint.

From accounting profit to corporation tax due

Every CT600 starts with your accounting profit before tax. AccLedger walks you through the standard adjustments — add-backs, capital allowances, reliefs, losses — with a clear running total so you understand exactly how the tax figure was reached.

  • Add-backs: depreciation, entertainment, fines, client gifts (and your own custom items)
  • Capital allowances: AIA, main pool WDA, special rate pool, FYA — per asset
  • R&D relief and patent box deductions
  • Trading losses brought forward applied with the loss-restriction rules
  • Other CT-allowable deductions captured as line items

Marginal relief, with associated companies

For accounting periods spanning the £50,000 small profits rate threshold and the £250,000 main rate, AccLedger calculates marginal relief at the standard fraction. If you have associated companies, the thresholds are divided automatically.

  • Tax before relief calculated at the right rate
  • Marginal relief computed using the 3/200 standard fraction (or current HMRC fraction)
  • Associated companies count entered once, applied across the calculation
  • Result shown gross and net of marginal relief

Close company loan tax (s455) — Box 505

If your company has a loan outstanding to a director or other participator at the year end, s455 CTA 2010 applies at 33.75%. AccLedger reads your director loan balance and pushes the figure into Box 505 — and reverses it when the loan is repaid in a future period.

  • s455 tax calculated at 33.75% of unpaid loan balance
  • Posted to Box 505 of the CT600
  • Reversal handled when the loan is repaid (within 9 months and a day for relief)
  • Director loan account view ties to the s455 figure

iXBRL accounts and computations included

HMRC requires accounts and computations submitted with the CT600 to be iXBRL-tagged. AccLedger generates both — your statutory accounts and your tax computation — fully tagged, and bundles them into the CT submission.

  • iXBRL-tagged statutory accounts (FRS 105 / FRS 102 1A)
  • iXBRL-tagged tax computation showing the profit-to-tax workings
  • CT600 form with every box populated from your data
  • Submission through the HMRC CT endpoint with full receipt logged

Designed for accountants managing many CT600s

Accountancy firms can prepare and submit CT600s for many client companies from one dashboard. Clients prepare their books in AccLedger, the accountant reviews and locks the period, runs the CT600 workings, and files. Sign-off is captured in-app.

  • Multi-client dashboard for the accountancy firm partner programme
  • Year-end checklist surfaces every adjustment that needs attention
  • Period locking after CT600 submission prevents retrospective edits
  • Submission history per client, with HMRC receipts

Frequently asked questions

Is AccLedger HMRC-recognised for corporation tax?
Yes. AccLedger is on HMRC's register of recognised CT software, submitting CT600 returns with iXBRL-tagged accounts and computations through the official endpoint.
Which capital allowances are supported?
AIA (Annual Investment Allowance), main pool writing-down allowance, special rate pool writing-down allowance, and First-Year Allowances (including the current full-expensing rules where applicable). You record additions and disposals per asset; AccLedger maintains the pool brought-forward balance.
How does marginal relief work?
For accounting periods where taxable profits fall between the small-profit rate threshold (£50,000) and the main-rate threshold (£250,000), corporation tax is charged at the main rate with marginal relief deducted, calculated using the standard fraction. AccLedger applies it automatically. Both thresholds are divided by the number of associated companies you record.
What is s455 close company loan tax?
s455 of CTA 2010 charges close companies a 33.75% tax on loans outstanding to a participator (typically a director-shareholder) at the year end, payable as part of the corporation tax bill. The tax is reclaimable when the loan is repaid. AccLedger calculates it from your director loan account balance and posts it to Box 505 of the CT600.
Can I claim R&D relief?
Yes. AccLedger captures the R&D claim figure (enhanced deduction for SME scheme, or RDEC for the merged scheme post-April-2024 reforms) and reflects it in your CT600 calculation. You will attach the supporting CT600L supplementary as required.
How are trading losses brought forward handled?
Trading losses brought forward are entered as part of the CT600 workings and applied against current-year profits with the loss-restriction rules respected (50% above the £5m allowance for groups). Carried-forward and current-year balances are tracked across periods.
Do I need separate iXBRL tagging software?
No. AccLedger generates the iXBRL-tagged statutory accounts and the iXBRL-tagged tax computation as part of the CT600 submission. There is no separate iXBRL tool to buy or operate.
Can my accountant prepare the CT600?
Yes. Invite your accountant or accountancy firm to AccLedger. They can prepare, review and submit the CT600 on your behalf. Accountancy firms with the partner programme manage many clients' CT600s from one dashboard.
What about associated companies?
Enter the number of associated companies in the CT600 settings. AccLedger divides the marginal relief thresholds (£50,000 lower / £250,000 upper) by the count when calculating tax due, in line with the post-April-2023 rules.
Can I file an amended CT600?
Yes. Amendments to a previously submitted CT600 are supported within HMRC's allowed window (typically 12 months from the filing deadline). The amendment is logged separately in your submission history.

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File your next CT600 with AccLedger

Every adjustment, every relief, every box on the form. From accounting profit to HMRC submission, in one place. Free for 90 days, no card.

Start your CT600See pricing

HMRC-recognised · 90-day free trial · From £10/month