New Director? Your First CT600 in 2026: The No-Jargon Guide

You've Started a Company. Now What About Corporation Tax?

Congratulations — you're a company director. Whether you've set up a limited company for freelancing, contracting, or launching a product, there's one unavoidable obligation: Corporation Tax.

Every UK limited company must file a CT600 return with HMRC, even if the company hasn't made a profit. This guide explains everything in plain English — what a CT600 is, when it's due, what goes in it, and how to file it without losing your mind.

What Is a CT600?

A CT600 is your company's tax return. It tells HMRC:

• How much money your company made
• What expenses it incurred
• How much Corporation Tax it owes (if any)

It's the company equivalent of a Self Assessment tax return — but instead of personal income tax, it covers Corporation Tax on your company's profits.

Important Distinction

Your personal tax (Self Assessment) and your company's tax (CT600) are completely separate. Being a director of a limited company means you may need to file both:

• CT600 — for the company, covering company profits
• Self Assessment — for you personally, covering your salary, dividends, and other personal income

This guide focuses on the CT600.

Key Dates Every New Director Must Know

When you incorporate a company, several tax clocks start ticking:

Corporation Tax Registration

HMRC should be notified within 3 months of your company starting to trade (not incorporation — trading). If you incorporated through Companies House, they may have notified HMRC automatically, but check. You can register at gov.uk.

Your First Accounting Period

Your first accounting period typically runs from your date of incorporation to your accounting reference date (usually the last day of the month in which you incorporated, one year later).

For example: incorporated on 15 May 2025 → first accounting period ends 31 May 2026.

However, your first period can be longer or shorter depending on when you chose your year-end. It cannot exceed 12 months for CT600 purposes (if it does, you'll file two returns).

Filing Deadline

Your CT600 is due 12 months after the end of your accounting period.

Payment Deadline

Corporation Tax is due 9 months and 1 day after the end of your accounting period — note this is before the filing deadline.

Missing either deadline results in penalties and interest, so put both in your calendar now.

What Goes Into a CT600?

The CT600 form has many boxes, but for a typical small company in its first year, you'll mainly deal with:

Income

• Turnover — the total amount your company invoiced (or received) during the period
• Bank interest — any interest earned on company bank accounts
• Other income — rare for new companies, but could include rental income or investment gains

Expenses

All allowable business expenses are deducted from income. Common ones for new companies:

• Director's salary and employer's National Insurance contributions
• Pension contributions (employer's contributions are tax-deductible)
• Office costs — rent, utilities, internet, phone
• Working from home allowance — if you work from home, the company can pay you up to £6/week tax-free (or the actual calculated cost)
• Software and subscriptions — accounting software, project management tools, etc.
• Professional fees — accountant, solicitor, formation costs
• Travel — business mileage (45p/mile for the first 10,000 miles)
• Insurance — professional indemnity, public liability
• Marketing — website, advertising, business cards

Capital Allowances

If your company bought equipment (computers, furniture, machinery), you generally can't deduct the full cost as an expense. Instead, you claim capital allowances:

• Annual Investment Allowance (AIA) — 100% relief on up to £1 million of qualifying equipment
• Full Expensing — 100% relief on qualifying plant and machinery (for companies)
• Writing Down Allowance — 18% or 6% per year for assets that don't qualify for full relief

For most new small companies buying a laptop and office furniture, the AIA covers everything at 100%.

Corporation Tax Rates (2025/26)

If your company has associated companies (other companies controlled by you or close associates), these thresholds are divided by the number of associated companies.

Most new directors' companies have profits well under £50,000 in the first year, so the 19% rate usually applies.

Use our corporation tax calculator to estimate exactly what you'll owe.

How to Actually File Your CT600

Since HMRC's free filing service closed on 31 March 2026, all CT600 returns must be filed using approved commercial software.

What You Need

1. Company's UTR — your Unique Taxpayer Reference (10 digits, sent by HMRC after Corporation Tax registration)
2. Government Gateway credentials — user ID and password for HMRC online services
3. Company accounts — at minimum, a profit and loss statement and balance sheet
4. Records of all income and expenses — ideally from accounting software or a well-maintained spreadsheet
5. Bank statements — for reconciliation

The Filing Process

With modern software like Taxpipe, the process works like this:

1. Sign up and add your company — enter your company number, and the software pulls details from Companies House
2. Answer guided questions — about your turnover, expenses, assets, and reliefs. No need to know which CT600 box is which
3. Review the calculations — the software computes your tax, including marginal relief if applicable
4. Check the generated accounts — iXBRL-tagged accounts are created automatically
5. Submit to HMRC — enter your Gateway credentials and submit directly
6. Save your confirmation — keep the HMRC receipt safe

The whole process typically takes 30 minutes to 2 hours for a straightforward first-year return, depending on how organised your records are.

Common First-Year Scenarios

"My company made a loss"

You still need to file a CT600. Report the loss — you can carry it forward to offset against future profits, potentially saving you tax in profitable years.

"I haven't traded yet"

If your company was incorporated but hasn't actually started business, you may need to file a nil return (a CT600 showing zero income and zero tax). Check with HMRC whether they expect a return for the period.

"I only paid myself dividends, no salary"

The dividends you take as a director are not a company expense — they're a distribution of profit. So they don't reduce your corporation tax bill. Many directors pay a small salary (up to the NIC threshold) plus dividends for tax efficiency.

"I bought a car through the company"

Company cars have special capital allowance rates:

• Electric vehicles: 100% first-year allowance
• Low emissions (≤50g/km CO₂): 100% first-year allowance
• Other cars: 6% or 18% writing down allowance depending on emissions

There are also Benefit-in-Kind (BIK) implications for your personal tax. Consider speaking to an accountant for vehicle purchases.

"I used my personal money for company expenses"

This is fine and very common. Record these as a director's loan — the company owes you money. When the company has funds, it repays you. There's no tax implication as long as the loan goes from director to company (the other direction — company lending to director — has tax consequences).

Do You Need an Accountant?

For a small, straightforward limited company — one director, simple trading, no complex transactions — many directors successfully file their own CT600 using software. It's what Taxpipe is designed for.

You might want an accountant if:

• Your company has complex transactions (international sales, R&D, multiple shareholders)
• You have associated companies
• You're unsure about specific tax reliefs you might be entitled to
• You simply don't want to deal with it (and that's perfectly valid)

Even if you use an accountant, it's worth understanding what a CT600 contains. You're legally responsible for its accuracy as a director.

Your First-Year Checklist

• Register for Corporation Tax within 3 months of trading
• Note your UTR when it arrives from HMRC
• Set up a record-keeping system (accounting software or detailed spreadsheet)
• Keep all receipts and invoices
• Note your accounting period end date
• Set calendar reminders for payment deadline (9 months + 1 day) and filing deadline (12 months)
• Choose your filing software (we'd love it if you chose Taxpipe)
• File your CT600 and pay any tax owed

Getting Started

Your first CT600 doesn't have to be intimidating. Modern software guides you through the process, and for most small companies the return is simpler than you'd expect.

Three things to do today:

1. Check you're registered for Corporation Tax at HMRC
2. Use our corporation tax calculator to estimate what you might owe
3. Sign up for Taxpipe — setting up takes 5 minutes, and you'll be ready when filing time comes

Filing your first CT600? Taxpipe makes it simple. Answer guided questions, we calculate your tax, generate iXBRL accounts, and submit to HMRC. See pricing or try the calculator.