How to file your Company Tax Return (CT600) online, start to finish

The deadlines

There are two dates for every accounting period, and the one for paying comes before the one for filing.

• Paying the tax has its own, earlier deadline: usually 9 months and one day after the end of the accounting period.^{(source 7)}
• The return is due 12 months after the end of the accounting period it covers.^{(source 8)}
• An accounting period for Corporation Tax can't be longer than 12 months, and is normally the same as the financial year your accounts cover.^{(source 9)}

A company's first year can need two returns rather than one. If that's you, read your company's first accounts and tax return before you start.

What you need before you start

• The company's accounts for the period, finished and approved. The return is worked out from them.
• The company's records for the period: sales, costs, bank statements, and anything it bought to keep, such as equipment.
• The dates of the accounting period the return covers.
• The company's Unique Taxpayer Reference.
• Software that can file the return.

The return carries the company's Unique Taxpayer Reference (UTR). It's on HMRC's letters, including the notice to file a return, and a limited company can request it online.^{(source 10)} HMRC write with the dates of the first accounting period after you add Corporation Tax to the company's business tax account.^{(source 11)} To file it with HMRC you need commercial software.^{(source 12)}

Filing it, step by step

1. 1

   Step 1: Get the books up to date for the whole period

   Every sale and every cost in the period, each with its document. The return can only be as right as the records under it, and this is the step that takes the time.

   Accounting records must include all money received and spent, the assets the company owns, the debts it owes or is owed, its stock at the year end, and the goods it bought and sold.^{(source 13)}

2. 2

   Step 2: Finish the accounts

   The return starts from the accounts' profit, so the accounts come first. For a small company that usually means micro-entity accounts for Companies House as well.

   The accounts and the tax return have different deadlines, but you may be able to send them at the same time.^{(source 14)}

3. 3

   Step 3: Work out the profit for Corporation Tax

   This is where the accounts' profit is adjusted into the figure HMRC tax. The computation has to show how each adjustment was made, from the accounts' own figures.

   It must include computations showing how the figures in the return were worked out from the figures in the accounts.^{(source 2)}

4. 4

   Step 4: Work out the tax, and pay it on time

   For a company with taxable profits of up to £1.5 million, the tax is due 9 months and 1 day after the end of the accounting period.^{(source 15)} If there is nothing to pay, tell HMRC, or they will send payment reminders. The return must still be filed.^{(source 16)}

5. 5

   Step 5: Complete the return and check every box

   The CT600 carries the company's details, the period, the figures from the computation and the tax. Read each box against the figure it came from before anything is sent.

   Supplementary pages, where a company needs them, form part of the return and are covered by its declaration.^{(source 17)}

6. 6

   Step 6: File it online, with the accounts and computations

   HMRC expect the return to be filed online.^{(source 18)} To file it with HMRC you need commercial software.^{(source 12)}

   Keep what was sent and what HMRC sent back. If a question ever comes, that's your answer.

If the return is late

Late filing penalties are charged even when there's no tax to pay.^{(source 19)}

GOV.UK sets the penalties out by how late the return is:

• 1 day late: £200.^{(source 20)}
• 3 months late: another £200.^{(source 21)}
• 6 months late: HMRC estimate the Corporation Tax bill and add a penalty of 10% of the unpaid tax.^{(source 22)}
• 12 months late: another 10% of any unpaid tax.^{(source 23)}

If the return is late 3 times in a row, the £200 penalties become £1000 each.^{(source 24)} Once a return is 6 months late, HMRC write with the Corporation Tax they think the company owes. That is a 'tax determination', and it can't be appealed.^{(source 25)}

If you are filing an overdue Company Tax Return, the steps above are the same; there's simply less time. The appeal route is below.

With a reasonable excuse you can appeal a late filing penalty online.^{(source 26)} You have to file the return before you appeal the penalty.^{(source 27)}

Common mistakes

• Treating the accounts' profit as the taxable profit. They are different figures, worked out differently.
• Paying on the filing date. The payment date comes first.
• Assuming a loss means nothing to file. A return is still due.
• Assuming a first year is one return. If the first accounts run longer than an accounting period can, it isn't.
• Leaving the records until the end. Rebuilding a year of receipts is slow, and the gaps are where mistakes happen.
• Waiting to look for the authentication code or the UTR until the deadline week.

Changes to a return usually have to be made within 12 months of the filing deadline.^{(source 28)}

How standing.tax helps

If you'd like help filing your company tax return without handing your records to someone else, this is what standing.tax does today:

• For a trading company, the Corporation Tax worked out from your books: the taxable profit, capital allowances on the equipment you list, losses carried forward, and the tax after marginal relief.
• Where the law leaves a choice to the company, such as which allowance to claim, the screen says what each option does and leaves the choice to you.
• The Company Tax Return (CT600) is built from the accounts Companies House accepted, so the two always match.
• If your company's return needs something standing.tax doesn't cover, it says so and gives the reason. It never guesses.
• A trading company's return can't be sent from standing.tax yet. The Corporation Tax screen tells you why, in a sentence.
• An email reminder 30 days and 7 days before your accounts, confirmation statement and Corporation Tax deadlines.
• You check and approve every figure. Nothing is filed until you have.

It won't tell you what to claim or how to arrange your tax. If you need that, it's one for an accountant, and standing.tax will say so when you reach it.