Filing Your First CT600

Step-by-step guide to filing your first CT600 corporation tax return with TinyTax. Covers company type selection, P&L entry, balance sheet, and HMRC submission.

Welcome! Filing your corporation tax return might sound daunting, but we'll walk you through it step by step. Most users complete their first filing in under 30 minutes.

Select your company type to customise this guide:

Trading Company

Property Company

Before You Start

You'll need:

Your company's profit and loss figures for the period
Your company's balance sheet figures (assets, liabilities, equity)
Your Company UTR (10-digit Unique Taxpayer Reference from HMRC - this is your company's tax reference, not your personal Self Assessment UTR)
Your HMRC Government Gateway login (the 12-digit ID and password you use for HMRC services)
If filing accounts too: Your Companies House WebFiling password (the 6-character code for your company)

ℹ Don't have a Company UTR? You would have received this when your company registered for Corporation Tax. Check your HMRC letters or call HMRC's Corporation Tax helpline on 0300 200 3410.

Step 1: Start Your Filing

From your dashboard, find the company you want to file for and click the button:

A dropdown appears - select CT600 (or CT600 and Accounts if you need both).

If you've already started a draft, you'll see:

⚠ Filing for the wrong company? If the wrong company appears after clicking, try logging out and back in. Make sure you're clicking the button on the correct row of your dashboard.

Step 2: Select Your Company Type

First, tell us what type of company you're filing for:

Company

What type of company is this?

Trading Company

Property Company

Dormant Company

Select the company type that matches your situation. This affects which fields appear.

Which should I choose?

Trading Company: Your company has been actively doing business (most common)
Property Company: Your company's main income is from rental properties
Dormant Company: Your company hasn't traded at all during this period

ℹ Your choice here affects which fields appear and how your tax is calculated. If unsure, "Trading Company" is usually correct for active companies.

Step 3: Confirm Your Accounting Period

Select the period you're filing for from the dropdown:

Accounting Period

The dates should match your company's financial year. If you don't see the correct period, check that it's not already filed or still in progress.

Extended Periods (Longer than 12 months)

⚠ Extended accounting period detected - this will require two CT600 submissions

If your period is longer than 12 months (common for first-year filings), don't worry! TinyTax automatically splits it into two returns:

Period 1: The first 12 months
Period 2: The remaining days

Your profits are apportioned automatically based on the number of days in each period. You'll submit both returns at the end.

Step 4: Enter Your Profit & Loss Figures

Enter your figures in whole pounds. The form has two columns - current year (required) and prior year (for comparison, often pre-filled from Companies House).

Profit & Loss


145Turnover
170Interest income
Total income
Cost of raw materials and consumables	(	)	(	)
Staff costs	(	)	(	)
Depreciation	(	)	(	)
Other charges	(	)	(	)
Total expenses	(	)	(	)
Profit before tax
Corporation tax	(	)	(	)
Profit for the year

Example P&L showing trading company figures. Costs are shown in parentheses.

The P&L follows the statutory micro-entity format. Here's what each field means:

Income

Field	What to enter
Turnover (Box 145)	Your total sales/revenue
Interest Income (Box 170)	Bank interest and similar

Field	What to enter
Property rental income (Box 145)	Total rent received from tenants
Interest Income (Box 170)	Bank interest and similar

Expenses

Field	What to enter
Cost of raw materials	Direct costs (materials, stock, consumables)
Staff costs	Salaries, wages, employer NI, pension contributions
Depreciation	Depreciation charged in your accounts
Other charges	All other business expenses (rent, insurance, subscriptions, etc.)

Field	What to enter
Cost of raw materials	Leave blank (typically £0 for property companies)
Staff costs	Property management staff, letting agents (if employed directly)
Depreciation	Depreciation charged in your accounts
Other charges	Property expenses: repairs, insurance, letting agent fees, mortgage interest, service charges

ℹ You can import figures from a trial balance CSV using the "Import" button. This auto-fills both P&L and Balance Sheet fields.

Step 5: Enter Your Balance Sheet

Enter your company's assets and liabilities at the period end date. The balance sheet shows what your company owns and owes.

Balance Sheet

Category
Fixed Assets
Total Current Assets
Creditors: amounts falling due within one year	(	)	(	)
Corporation Tax Payable	(	)	(	)
Net Current Assets
Net Assets

Share Capital
Retained Earnings
Shareholders' Funds

Example Balance Sheet. Liabilities are shown in parentheses. Net Assets must equal Shareholders' Funds.

What to enter in each section:

Assets - What your company owns

Fixed Assets: Equipment, vehicles, computers, property - things you keep for more than a year
Total Current Assets: Bank balances, cash, money owed by customers, stock

Liabilities - What your company owes

Creditors (within 1 year): Unpaid supplier bills, credit cards, short-term loans
Corporation Tax Payable: Tax owed to HMRC (auto-calculated from your P&L)
Creditors (after 1 year): Bank loans, director's loans, mortgages

Equity - The company's value to shareholders

Share Capital: The value of shares issued (often £1, £100, or £1,000 for small companies)
Retained Earnings: Accumulated profits less dividends (calculated automatically)

ℹ Prior year values are automatically fetched from Companies House when available. You'll see "Prior year data loaded" when this happens.

Step 6: Complete the Tax Computation

Your accounting profit needs adjusting for tax purposes. TinyTax calculates this automatically in the Tax Computation section:

Tax Computation - Current Year

Show all

Trading profit before tax
Add back: Depreciation (disallowable for tax)
Add back: Disallowable expenses
Less: Annual Investment Allowance	()
165Net trading profits

Corporation Tax Calculation

315Profits chargeable to corporation tax
Tax @ 19%
440Corporation Tax Payable

The tax computation shows how your accounting profit is adjusted for tax purposes. Box numbers correspond to CT600 form fields.

Key adjustments:

Depreciation is added back (it's disallowed for tax - capital allowances are used instead)
Disallowable expenses like client entertaining are added back
Annual Investment Allowance (AIA) is deducted for equipment purchases (up to £1 million)

The result is your Net Trading Profits (Box 165), which flows into your Corporation Tax calculation.

Key adjustments for property companies:

Depreciation is added back (it's disallowed for tax - capital allowances are used instead)
Disallowable expenses like property improvements (not repairs) are added back
Property income flows into Box 170 (Total rents and other income from land and property)

The result is your Property Income (Box 170), which flows into your Corporation Tax calculation. Note: Property companies don't have "trading profits" - they have property income instead.

Step 7: Complete the Declaration

The declaration section identifies who is signing the return on behalf of the company:

Tax Return Declaration

Person Making Declaration*

Position/Status*

Company UTR*

The declarant must be authorised to sign on behalf of the company. The UTR is your 10-digit Corporation Tax reference from HMRC.

Field	What to enter
Person making declaration	Select a director from the dropdown, or choose "Other" to enter manually
Position/Status	Their role (e.g., "Director") - auto-filled when you select from dropdown
Company UTR	Your 10-digit HMRC Corporation Tax reference

⚠ The Company UTR is your company's Corporation Tax reference (10 digits). This is NOT your personal Self Assessment UTR which you'd use for individual tax returns.

Step 8: Review Your Submission

Click the button at the bottom of the form:

On the preview page, you'll see:

A summary of your profit & loss
A summary of your balance sheet
Your Tax Computations document (the detailed calculation)
Your CT600 ready for submission

Ready to Submit

Take a moment to check:

Are the figures correct?
Is the tax calculation what you expected?
Is the right company showing?

Use this to go back and change anything.

Step 9: Submit to HMRC

When you're ready, click:

A popup will ask for your HMRC Government Gateway credentials:

Field	What to enter
Company UTR	Your 10-digit Corporation Tax reference (pre-filled from the form - you can edit it here if needed)
Government Gateway ID	Your 12-digit user ID
Password	Your Government Gateway password

ℹ This is the same login you'd use on the HMRC website. If you've forgotten it, you can recover it at gov.uk.

ℹ Entered the wrong UTR on the form? You can correct it directly in this popup without going back - just edit the Company UTR field before submitting.

Click Submit and wait a few seconds. You'll see:

Submitted to HMRC

Then, once HMRC accepts it:

Accepted by HMRC

✓ Your CT600 has been submitted successfully!

Step 10: Submit Accounts (If Required)

If you also need to file accounts with Companies House, you'll see a second button:

Enter your Companies House Authentication Code - the 6-character code for this specific company.

⚠ Each company has its own auth code! The code for Company A won't work for Company B. Request a new code at gov.uk/file-your-company-annual-accounts if needed.

What Happens Next?

After submitting:

HMRC processes your CT600 - Usually accepted within minutes
Pay any tax due - HMRC will send a payment reference (or check your HMRC online account)
Companies House processes accounts - Usually accepted within 24-48 hours
Keep your records - You can download copies from your TinyTax dashboard

Common Issues

"I can't find my draft - where's the save button?"

Good news: TinyTax auto-saves your progress. There's no save button because you don't need one!

To get back to your draft:

Go to your Dashboard
Find the company
Click

Your figures will be right where you left them.

"The wrong company appears when I click File"

This usually happens if you have multiple companies. Try:

Log out and log back in
Use the company selector dropdown at the top of the form
Make sure you're clicking the correct row on your dashboard

"My period is longer than 12 months - what do I do?"

Nothing special! TinyTax automatically detects extended periods and creates two CT600 returns for you. Just enter your figures once, and we'll apportion them correctly between the two periods.

"My Companies House auth code isn't working"

The auth code is a 6-character code specific to each company. Common issues:

Wrong code: Each company has its own code - check you're using the right one
Expired code: Codes expire after 28 days - request a new one from Companies House
Typo in code: The code is case-insensitive but must be exactly 6 characters

Request a new auth code at gov.uk

"HMRC rejected with Error 3001 - original already received"

This error means HMRC already has a CT600 for this period. You probably need to file an amended return instead of a new one.

See our guide: Filing an Amended CT600

"Can I file for a CIC or Company Limited by Guarantee?"

CICs (Community Interest Companies): Yes! HMRC accepts CT600 from CICs via TinyTax. However, you'll need to file your accounts directly with Companies House (CICs have additional reporting requirements).

CLGs (Companies Limited by Guarantee): Yes, TinyTax supports these.

"How do I claim capital allowances?"

If you have equipment, vehicles, or other assets that qualify for capital allowances (like the Annual Investment Allowance), enter them in the Tax Adjustments section. The form will calculate your allowances automatically.

Property companies can claim capital allowances on qualifying items like:

Furniture and white goods in furnished lettings
Equipment used to manage properties
Replacement of domestic items (for residential lets)

Enter these in the Tax Adjustments section under Annual Investment Allowance. Note: You cannot claim capital allowances on the property itself - only on qualifying fixtures and equipment.

Still Need Help?

We're here for you! Post a question in our community forum or email us at hello@tinytax.co.uk.

Last updated: 12 December 2025

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