Accounting

Accounts & tax returns

Corporation tax returns

Corporation Tax is charged on the taxable profits of UK companies, and the company tax return, the CT600, is the document that reports those profits and the tax due to HMRC. Taxable profit is not the same as the profit in the accounts: the computation starts with accounting profit, adds back expenses the tax rules do not allow, deducts capital allowances in place of depreciation, applies loss relief and other claims, and arrives at the figure to which the rate is applied. The return must be filed within twelve months of the accounting period end, and the tax paid within nine months and one day, which is the deadline most companies actually need to plan around.

from £199 · fixed, per return

Next deadlines

  • Company tax return (CT600) due 12 months after your year end (a 31 December year end files by 31 December)
  • R&D claim deadline: 2 years after the end of the accounting period (and the pre-notification window of 6 months after the period for first-time claimants)
  • Companies House accounts due 9 months after your year end (a 31 December year end files by 30 September)
  • Corporation Tax payment, 9 months and 1 day after your year end (a 31 December year end pays by 1 October)

Fees

Packages, fixed and published

included in accounts packages

CT600 with accounts prepared by us

£199

Standalone CT600 from your accounts

£299

CT600 with capital allowances review

£279

Overdue CT600 rescue

Who this is for

Corporation Tax

Limited companies in the UK of every size below the large-company regime: companies whose accounts are prepared by another firm or in-house and need the tax return filed, companies with capital expenditure to claim, companies that have made a loss and want it used well, groups of associated companies, and companies whose CT600 is already overdue.

What is included

Inside the fixed fee

  • Corporation Tax computation reconciling accounting profit to taxable profit, with every adjustment explained
  • Capital allowances claimed in full: annual investment allowance, full expensing, writing-down allowances and the special rate pool
  • Loss relief planned and claimed: carry back, carry forward and group relief where it applies
  • Marginal relief and associated-company rules applied correctly between the 19% and 25% rates
  • CT600 with supplementary pages, iXBRL-tagged accounts and computation, filed electronically with HMRC
  • Payment note with amount, due date and HMRC reference, and reminders before the payment and filing dates

In detail

How corporation tax works

Since April 2023 there have been two rates. Profits up to £50,000 pay the small profits rate of 19%; profits over £250,000 pay the main rate of 25%; and between the two, marginal relief tapers the effective rate upwards, meaning each pound of profit in the band costs 26.5p in tax. The thresholds are shared between associated companies, so a director who controls two companies has half the thresholds for each, and a group of five has a fifth. We check the associated-company position on every return, because it is the single most common cause of underpaid Corporation Tax in owner-managed businesses, and HMRC charges interest from the original due date when it is caught.

Capital allowances are where most of the tax value lies for companies that invest. The annual investment allowance gives 100% relief on up to £1 million of plant and machinery each year. Full expensing gives 100% first-year relief on new and unused main-rate assets with no cap, and 50% on special-rate assets. Cars are excluded from both and go into pools written down at 18% or 6% depending on emissions, with zero-emission cars qualifying for 100% first-year relief. Integral features of buildings, such as electrical and heating systems, go into the 6% pool. Our £299 package reviews every asset purchased in the year against these rules and claims the maximum, and in a year of significant investment the difference between a careful and a casual claim can run to thousands of pounds of tax.

Losses need planning too. A trading loss can be relieved against other profits of the same period, carried back twelve months to recover tax already paid, or carried forward against future profits of the same trade, with the choice depending on cash flow and the expected profit profile. Terminal losses on cessation can be carried back three years. The computation also handles the deductions companies routinely miss: employer pension contributions paid in the period, the research and development relief now claimed under the merged scheme, and the correct treatment of director's loan write-offs and interest. Every adjustment is listed in the computation you receive, with a one-line explanation, so the route from the accounts to the tax figure is transparent.

Filing is electronic and requires the accounts and the computation to be tagged in iXBRL, which we produce and validate. Where we have prepared the accounts the CT600 is included in the accounts fee; where another firm or your own team has prepared them, the standalone return is £199, with the capital allowances review at £299 and an overdue rescue at £279 that includes a reasonable-excuse appeal where the facts support one. Once you approve the return it is filed, HMRC's acknowledgement is forwarded, and you receive a payment note with the amount, the due date and your seventeen-character payment reference, which changes for every accounting period and is a frequent source of misallocated payments when typed by hand.

Process

From first message to filed

  1. Scope the job

    We find out what you need filed, when it is due and what state the records are in, and tell you which fixed-fee package applies.

  2. Agree the price

    The fee is confirmed in writing. There is no hourly billing and nothing added for questions during the work.

  3. Hand over the records

    Photographs, PDFs, software access or a spreadsheet, sent however suits you. We confirm what we have and what is missing within two working days.

  4. Approve, then we submit

    You review the draft with our explanation, sign off, and we file. Receipts, copies and the next deadlines come back to you immediately.

Worth knowing

Rules that come up in this work

Allowable expenses

The expenses sole traders most often miss are home working costs, claimed by actual proportion or HMRC's flat rate, the business share of phone and internet, mileage at 45p for the first 10,000 business miles, and training that maintains existing skills. The ones most often claimed wrongly are commuting, entertaining customers and clothes that could be worn outside work.

Record keeping

Record keeping is a legal obligation with a penalty of up to £3,000 for failure, but its real value is in making every other filing cheaper and more defensible. Keep invoices, receipts, bank statements, mileage logs and any HMRC correspondence, digitally if you like, for five years after the relevant filing deadline for individuals and six years for companies and VAT.

The 60-day property CGT return

The 60-day Capital Gains Tax return on residential property is the deadline landlords most often miss, because it falls outside the Self Assessment cycle and runs from completion, not exchange. Private residence relief for periods you lived in the property, plus the final nine months, reduces the gain. Penalties for a late return mirror Self Assessment, starting at £100.

Crypto records and reporting

Crypto tax splits into capital gains on disposals and income on rewards, with different rates and different reporting. The £3,000 annual exempt amount and the 18% and 24% rates apply to gains; staking, mining and airdrop income is taxed at marginal income tax rates. HMRC's nudge letters to holders have increased sharply, and a voluntary disclosure before one arrives is treated far more leniently.

The trading and property allowances

Small side incomes are covered by two £1,000 allowances, one for trading and one for property, which remove the need to register or report income below that level. Once income exceeds £1,000, the allowance can be used in place of expenses, a choice worth making deliberately: a freelancer with £900 of costs is better off with the allowance, one with £3,000 is not.

Dormant companies

Dormancy is a status that is easy to lose. The strict rule is no accounting transactions other than share capital and Companies House fees, which means no bank account activity at all in practice. Fees should be paid personally by the director. A company that traded and has stopped becomes dormant only after its final trading accounts and tax return are filed and HMRC is told.

Workplace pensions and auto-enrolment

Auto-enrolment duties begin the day you take on your first employee, not when the Pensions Regulator writes to you. Eligible staff must be enrolled, contributions paid every pay period and re-enrolment carried out every three years. Director-only companies without employment contracts are usually exempt. Fines for non-compliance are fixed and escalating.

Questions

Corporation Tax: your questions answered

Is the CT600 included when you prepare the accounts?

Yes. Our limited company accounts packages at £299 and £449 include the computation, the CT600 and filing with HMRC. The standalone fees on this page are for companies whose accounts are prepared elsewhere or where the return needs separate work such as a capital allowances review.

What are the Corporation Tax rates for 2026/27?

Profits up to £50,000 are taxed at the 19% small profits rate. Profits above £250,000 pay the 25% main rate. Between the two, marginal relief produces an effective rate rising from 19% towards 25%, with a marginal rate of 26.5% on each pound in the band. The thresholds are divided by the number of associated companies plus one.

When is Corporation Tax paid and the return filed?

Tax is due nine months and one day after the end of the accounting period; the CT600 is due twelve months after it. Companies with profits over £1.5 million pay by instalments instead. Interest runs on late payment from the due date, and a late return attracts a £100 penalty rising to 10% of the tax at twelve months.

What are capital allowances and what can I claim?

Capital allowances are the tax equivalent of depreciation. The annual investment allowance gives 100% relief on up to £1 million of qualifying plant and machinery a year; full expensing gives 100% on new main-rate assets without limit; cars and integral features go into pools at 18% or 6%. The £299 package reviews every asset purchase in the year.

My company made a loss. What can be done with it?

A trading loss can be set against the company's other profits of the same year, carried back one year for a repayment of tax already paid, or carried forward against future profits. The right choice depends on cash flow and expected profits. We model the options and make the claim on the return.

What are associated companies and why do they matter?

Companies under common control count as associated, and the £50,000 and £250,000 thresholds are divided between them. A director who owns two companies has thresholds of £25,000 and £125,000 for each. Missing this is a common error that produces an underpayment and interest.

Are dividends and salary treated differently for Corporation Tax?

Yes. Salary, employer National Insurance and employer pension contributions are deductible expenses that reduce taxable profit. Dividends are paid from profit after tax and are not deductible. This asymmetry is central to the salary-versus-dividend planning we do for directors.

What expenses are not allowed for Corporation Tax?

Business entertainment of customers, most fines and penalties, depreciation (replaced by capital allowances), general provisions, and the private element of mixed-use costs. Legal fees on capital items are also disallowed. The computation adds these back to accounting profit and we list every adjustment so you can see the effect.

What is iXBRL and do I need to worry about it?

HMRC requires the accounts and computation attached to a CT600 to be tagged in iXBRL, a machine-readable format. We produce and validate the tagged files as part of the service. If another firm prepared your accounts we tag their figures; you never deal with it directly.

My CT600 is overdue. What now?

The £279 rescue fee gets it prepared and filed quickly from your accounts. The £100 late penalty is fixed, rising to £200 after three months and then to tax-geared penalties at six and twelve months, so speed matters. If there is a reasonable excuse we draft the appeal as part of the fee.

Does R&D affect my Corporation Tax return?

Yes. Research and development relief is claimed on the CT600 and reduces the tax or generates a credit. Since the merged scheme, first-time claimants must notify HMRC within six months of the period end. Our R&D service prepares the technical report and the computation; the claim then goes on the return we file.

Can you deal with HMRC if they open an enquiry into the return?

Yes. As your authorised agent we receive and respond to HMRC correspondence. Routine queries about a return we filed are handled at no extra charge. A formal enquiry is handled through our HMRC investigation service at fixed fees per stage, so you know the cost before deciding how to proceed.

Get corporation tax for a fixed fee

Tell us what you need. You get one fixed fee in writing, and nothing is filed until you approve it.

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