CT600 Filing Checklist — Everything You Need Before You Start

Before you start your CT600, get everything in one place. This checklist covers every document and figure you'll need — nothing worse than getting halfway through your return and realising you're missing your UTR.

Print this page or keep it open in another tab. Tick things off as you go.

1. Company details

• Company Registration Number (CRN) — 8-digit number from Companies House (e.g., 12345678, SC123456, NI123456)
• Unique Taxpayer Reference (UTR) — 10-digit number from HMRC (e.g., 1234567890). Check your original HMRC letter or your Government Gateway account
• Company name — exactly as registered at Companies House
• Registered office address — the address on your Companies House filing, not your trading address
• SIC code — your Standard Industrial Classification code (e.g., 62020 for IT consultancy). Find it on your Companies House record
• Accounting period dates — the exact start and end dates. These must match what HMRC has on file

Where to find your UTR: Log into your HMRC Government Gateway account, check previous correspondence from HMRC, or call 0300 200 3410.

2. Income figures

• Total turnover/revenue — all sales income for the accounting period
• Bank interest received — even small amounts must be declared
• Other income — rental income, investment income, grants, COVID support scheme payments
• Dividends received from UK companies — not taxable but must be reported in certain boxes

Important: Use figures for the exact accounting period on your CT600, not your calendar year or VAT quarter.

3. Expense figures

Break your expenses into these categories:

Trading expenses

• Cost of sales — direct costs of goods/services you sold
• Employee costs — salaries, employer's NI, pension contributions, benefits
• Premises costs — rent, rates, utilities, insurance, repairs
• Travel and subsistence — business travel only (not home to office commuting)
• Professional fees — accountant, solicitor, consultancy (not tax penalty fees)
• Office costs — stationery, postage, phone, software subscriptions
• Marketing and advertising — website, Google Ads, print materials
• Insurance — professional indemnity, public liability, employer's liability
• Training — courses and conferences directly related to your current trade
• Bank charges and interest — on business accounts and loans

Use of home as office

• Simplified method: £6 per week (£312/year for 52 weeks) — no receipts needed
• Actual cost method: Proportion of household bills (heating, electricity, broadband, mortgage interest/rent) based on room usage and time

Disallowable expenses (add back to profit)

• Client entertaining — meals, drinks, events with clients (never deductible)
• Depreciation — the accounting charge for asset wear (replaced by capital allowances)
• Personal expenses — anything put through the company that isn't wholly and exclusively for business
• Fines and penalties — parking tickets, HMRC penalties, court fines
• Non-trade charitable donations — claimed separately in the CT600, not as an expense

4. Capital items

If you bought or sold any business assets during the period:

• Plant and machinery purchased — computers, office equipment, tools, furniture
• Vehicles purchased — note the CO2 emissions (affects capital allowance rate)
• Assets sold or scrapped — original cost and sale proceeds
• Brought-forward capital allowance pools — from last year's CT600 (if applicable)

For most small companies: Claim Annual Investment Allowance (AIA) on everything except cars — 100% of the cost, up to £1 million.

5. Directors and shareholders

• Director's salary — gross amount paid during the period
• Director's employer NI — the employer's share of National Insurance
• Dividends declared — amounts and dates of any dividends paid
• Director's loan account balance — if the director owes money to the company (or vice versa), you may need to complete additional CT600 boxes
• Number of associated companies — other companies controlled by the same people (affects your tax rate thresholds)

6. Tax payments and reliefs

• Corporation tax already paid — payments on account for this period
• Tax overpaid from previous periods — any credits carried forward
• R&D expenditure — if claiming R&D tax credits (specialist advice recommended)
• Losses brought forward — trading losses from previous periods you want to set against this period's profits
• Gift Aid donations — made by the company (claimed as a deduction in the CT600, not as an expense)
• Patent Box election — if applicable

7. Previous year's CT600 (if not your first return)

• Last year's tax computation — to check consistency and brought-forward figures
• Capital allowance pools — written-down values to carry forward
• Loss memorandum — any unused losses
• HMRC amendments or enquiries — anything HMRC queried on previous returns

8. Filing details

• Government Gateway credentials — user ID and password for online submission
• Filing deadline — 12 months after accounting period end
• Payment deadline — 9 months and 1 day after accounting period end
• Payment reference — UTR + accounting period end (e.g., 1234567890A2503)

Key deadlines at a glance

Quick sanity checks before filing

Before you hit submit, verify:

1. Profit figure makes sense — compare to last year. If it's wildly different, check your figures
2. Tax rate is correct — 19% for profits under £50k, 25% for over £250k, marginal relief in between
3. Accounting period matches — the dates on your CT600 must match HMRC's records exactly
4. iXBRL accounts are included — HMRC requires accounts in iXBRL format since 2011
5. All income is declared — bank interest, grants, and other income are commonly forgotten
6. Capital allowances are claimed — don't leave money on the table
7. Disallowable expenses are added back — entertainment, depreciation, personal costs

Ready to file?

Once you have everything on this checklist, the actual CT600 filing takes about 15 minutes with Taxpipe. We ask the questions in plain English, calculate your tax automatically, generate iXBRL accounts, and submit directly to HMRC. Start your CT600 now → No accountancy knowledge needed. £59 one-time fee. Money-back guarantee.

Related Articles

• HMRC Rejected Your CT600? Common Errors and How to Fix Them
• Disallowable Expenses for Corporation Tax (Full List)
• CT600 Filing Agent Authorisation with HMRC

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Related: CT600 box-by-box guide