Three clocks, three shapes, one thing in common
None of these tell you what you owe. They tell you when HMRC has to be told you exist. That is the quieter deadline, and it generates a penalty nobody was expecting.
Self-employment: 5 October, and the notice you get depends on the month
The rule is the 5 October after the end of the tax year in which you started. It is fixed, it is simple, and its consequence is not.
Start trading on 10 April and the tax year you are in does not end until the following 5 April, so you have until 5 October after that: about eighteen months. Start on 1 March and the year ends five weeks later, so the same rule gives you about seven months.
Nothing warns you which side you are on, and the shorter one is the version most people accidentally pick, because a lot of businesses start in the new year.
The £1,000 is gross, which is not the number in your head
Below £1,000 of trading income you may not have to register at all. It is measured before any expenses, so £1,400 of takings with £600 of costs is over it even though the profit is not.
You would still register if you want to claim a loss, keep a National Insurance record going voluntarily, or claim Tax-Free Childcare or Maternity Allowance on that income. And the allowance does not reach income from a partnership, or from a company you or somebody connected to you controls.
PAYE: a window with both ends shut
Register before the first payday. Also, you cannot register more than two months before you start paying people.
Those two facts together are the trap, and they specifically punish the person who plans ahead. Sort it out in January for an April start and you will be turned away, and by the time the window opens the thing you were trying to buy, time, has gone.
There is no published turnaround for the reference. gov.uk used to give one and now points at its own "when to expect a reply" service, which moves. What does not move is that you cannot send a Full Payment Submission without the reference, and an FPS is due on or before the day somebody is paid. Diary the opening date, not the payday.
A director on a salary is an employer
A one-person company paying its director through PAYE registers exactly like anybody else. Dividends are not pay and do not trigger it.
Which is why a company can run for a year with no PAYE scheme at all and then need one in the month the director decides to put themselves on the payroll, with the same two-month window everybody else has.
Corporation Tax runs from active, not from incorporation
Section 55 of the Finance Act 2004 asks for notice within three months of the accounting period beginning, and a Corporation Tax accounting period begins when the company comes within the charge. That is the day it becomes active.
Incorporate in January, start trading in June, and the deadline is September. Counting three months from the incorporation date gives April, which is both too early and the wrong question.
Most companies never meet this, because registering at Companies House sets Corporation Tax up at the same time. The ones that do are formed dormant and switched on later: shelf companies, and the very common "I set one up last year in case I needed it".
Dormant is a description, not a setting
Active is wider than trading. Carrying on a business activity, buying and selling with a view to profit, providing services, earning interest, managing investments, receiving any other income.
Interest on a company bank account will do it. A company that holds a property and takes nothing may be dormant; the day the first rent arrives, it is not, and three months start running from that day rather than from the day anybody thinks about it.
Late is negotiable, and the lever is who spoke first
A non-deliberate failure to notify starts at 30% of the tax that went unpaid because of it. Paragraph 13 of Schedule 41 then lets HMRC reduce that for the quality of the disclosure, and the floors are published.
Tell them yourself, while HMRC has known about the failure for less than twelve months, and the minimum is nil. Tell them after they have asked, in the same window, and the floor is 10%. Outside twelve months those become 10% and 20%.
So the answer to realising you are late is not to hope. It is to raise it yourself.
Common questions
Is the self-employment deadline 5 October or 31 January?
Both, and they are different jobs. 5 October is when you tell HMRC you exist, and it is the 5 October after the tax year you started trading in ends. 31 January is when the return goes in and the tax is paid, and it is the January after that October. Mixing them up costs money in both directions: people register in a December panic for a year that has not closed, and people sail past October holding the January date in their head.
I started trading in March. When do I register?
By 5 October the same year, because the tax year ended on 5 April a few weeks after you started. Somebody who started on 10 April, five weeks later, has until 5 October the following year. That is eighteen months against seven, from the same rule, and nothing on gov.uk warns you which side of it you are on.
Do I have to register if I only made a few hundred pounds?
Probably not. The trading allowance is £1,000 of gross income a year, measured before any expenses come off, and under it you may not need to register at all. You would still register if you want to claim a loss, pay voluntary Class 2 National Insurance, or claim Tax-Free Childcare or Maternity Allowance on that income. It also does not apply to income from a partnership or from a company you or somebody connected to you controls.
How early can I register as an employer?
Not more than two months before you start paying people, and you must be registered before the first payday. That is a window with both ends shut, and it punishes the organised: sorting it out in January for an April start does not work. gov.uk no longer publishes a turnaround for the reference, so plan on it not being instant and diary the opening date rather than the payday.
I have already paid somebody without a PAYE reference. What now?
Register, run the payroll, keep the payment submission, and send a late Full Payment Submission once the reference arrives. That is HMRC's own instruction on the registration page rather than a workaround somebody invented. You cannot send an FPS without the reference, which is the whole reason the sequence is that way round.
Is Corporation Tax three months from incorporating?
No. It catches shelf companies. Section 55 of the Finance Act 2004 wants notice within three months of the accounting period beginning, and that period begins when the company comes within the charge, which means when it becomes active. A company incorporated in January and trading from June notifies by September, not April. Registering at Companies House usually sets Corporation Tax up at the same time, so the ones that get caught are formed dormant and switched on later.
What counts as the company being active?
Wider than trading. HMRC lists carrying on a business activity, buying and selling with a view to profit, providing services, earning interest, managing investments, or receiving any other income. Bank interest on a company account is enough. A company holding a property and receiving nothing may be dormant; the day it takes rent, it is not.
I am already late. How bad is it?
Less bad if you move first. Schedule 41 to the Finance Act 2008 starts a non-deliberate failure to notify at 30% of the tax at stake, and paragraph 13 sets the floor by how the disclosure was made. Unprompted, where HMRC has known about the failure for under twelve months, the floor is nil. Prompted, in the same window, 10%. Outside twelve months it is 10% and 20%. The difference between paying nothing and paying something is who spoke first.