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Not financial advice: this guide is general information to help you understand the basics. It is not financial, tax or legal advice. Rules and figures can change, so check the linked official pages, and speak to an accountant or adviser about your situation.
Missing a deadline is one of the most avoidable mistakes in a new business, and it can cost you money even if you owe no tax at all. This guide sets out the main dates and thresholds for sole traders and limited companies in plain English. Every figure was checked on GOV.UK or the British Business Bank on 29 October 2026. Rules can change, so always check the linked page before you rely on a date.
If you are a sole trader: Self Assessment
Register by 5 October
If you need to send a Self Assessment tax return and have not sent one before, GOV.UK says you must register by 5 October after the end of the tax year you need to send a return for. The tax year runs from 6 April to 5 April. So if you started trading in, say, the 2025 to 2026 tax year, the deadline to register was 5 October 2026. Registering also gets you a Unique Taxpayer Reference (UTR), which the British Business Bank’s accountant guidance says usually arrives by post.
File online by 31 January
GOV.UK gives the deadline for online tax returns as 31 January after the end of the tax year. Paper returns have an earlier deadline of 31 October. The deadline to pay the tax you owe is also 31 January.
The £100 late filing penalty
GOV.UK says you will get a penalty of £100 if your tax return is up to 3 months late. It adds that you will have to pay more if it is later, or if you pay your tax bill late. You can also be charged interest on late payments. The £100 applies even if you have no tax to pay, so filing on time matters even in a quiet first year.
VAT: the £90,000 threshold
VAT applies to sole traders and companies alike. GOV.UK says you must register if your total taxable turnover for the last 12 months goes over £90,000, or if you expect it to go over £90,000 in the next 30 days. If you go over it in the past 12 months, you have to register within 30 days of the end of the month in which you went over. You can choose to register voluntarily below the threshold. The British Business Bank’s accountant guidance notes some smaller businesses do this to reclaim VAT on purchases and expenses. Turnover means sales, not profit, so keep a running 12-month total rather than looking only at the tax year.
If you run a limited company
Corporation Tax: register within 3 months of trading
When you register your company with Companies House, GOV.UK says you get the option to be set up for Corporation Tax at the same time. If you do not, you need to add Corporation Tax to your business tax account. The British Business Bank’s accountant guidance says you must register with HMRC for Corporation Tax within three months of trading.
GOV.UK gives the main rate as 25% for profits over £250,000, and a small profits rate of 19% for profits of £50,000 or less, with Marginal Relief possible in between. You do not get a bill: you work out, pay and report the tax yourself, often with an accountant.
Key company deadlines
GOV.UK lists these deadlines for private limited companies:
- First accounts to Companies House: 21 months after the date you registered with Companies House.
- Annual accounts to Companies House: 9 months after your company’s financial year ends.
- Pay Corporation Tax (or tell HMRC you owe none): 9 months and 1 day after your accounting period ends, for taxable profits up to £1.5 million.
- Company Tax Return: 12 months after your accounting period ends.
Note that tax is due before the return. Many founders get caught by this.
Companies House basics
- Confirmation statement: every company, including dormant ones, must file one at least once every 12 months, confirming the information Companies House holds is up to date. You can file up to 14 days after the review period ends. GOV.UK says the fee is £50 online, and that failing to file can lead to a fine of up to £5,000 and the company being struck off.
- Identity verification: GOV.UK says all directors must verify their identity before a confirmation statement can be accepted.
- Keep your details current: tell Companies House about changes to directors, people with significant control, and your registered office or email address.
- Keep records: GOV.UK says company records must normally be kept for 6 years from the end of the financial year they relate to, and that HMRC can fine you £3,000 if you do not keep accounting records.
How to stay on top of it
- Put every deadline in your calendar now, with a reminder a month before.
- Sign up for Companies House email reminders.
- Set aside money for tax as you are paid, ideally in a separate pot. Our guide to separating your money explains how.
- Keep a running 12-month sales total to watch the VAT threshold.
- Consider an accountant. The British Business Bank’s guidance covers how one can help.
Knowing your costs makes tax easier to plan. Our card reader fee calculator shows what card fees take from your takings, and our pricing guide explains how to include VAT and fees in your prices.
Sources
- GOV.UK: Register for Self Assessment
- GOV.UK: Self Assessment deadlines
- GOV.UK: Self Assessment penalties
- GOV.UK: When to register for VAT
- GOV.UK: Corporation Tax
- GOV.UK: Corporation Tax rates
- GOV.UK: Accounts and tax returns for private limited companies
- GOV.UK: Filing your company's confirmation statement
- GOV.UK: Company and accounting records
- British Business Bank: Top business tips from an accountant
Free official help and our tools
- GOV.UK: Business and self-employed
- British Business Bank: Business guidance
- Start Up Loans: Support and guidance
- Our card reader fee calculator
- Our Find my card reader quiz
More free guides
- Pricing for profit
- Separating business and personal money
- Marketing on a small budget
- Legal setup
- Data protection & licences
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Last checked 29 October 2026. Spotted something out of date? Let us know.