Tax deadlines UK for small businesses need to know in 2025
When you run a small business in the UK, you already have a lot on your plate.
Keeping customers happy, staying on top of your accounts, and planning for growth, etc. With all that fighting for your attention, tax deadlines can easily slip your mind. And missing one deadline can lead to fines and extra stress that you don’t need.
The truth is, tax dates are a part of keeping your business running smoothly. With 2026 coming up fast, knowing exactly what’s due and when will make life a whole lot easier.
Let’s have a look at them, shall we?
Tax deadlines UK for small businesses
Self Assessment tax return deadlines 2025
Self Assessment tax returns are a staple of small business life in the UK—but the deadlines often trip up busy traders and freelancers.
If you operate as a sole trader or a partner in a business, here are the 2025 Self Assessment deadlines you can’t ignore:
31 January 2025: Deadline for filing your Self Assessment online and paying your tax bill from the previous financial year (2023–24).
31 July 2025: Deadline for paying your second Self Assessment payment on account.
Making Tax Digital (MTD) isn’t currently applied to Self Assessment for most sole traders—but it's always good to double-check, as the rules may evolve.
What you need to know:
You must file your online return and pay what you owe by 31 January. If you miss this, you face a £100 late filing penalty immediately, plus extra fines and interest if you don’t pay or file soon after.
Payments on account are advance tax payments based on your previous year’s bill, due by 31 July and again on 31 January.
Simple tools like Xero or QuickBooks can help you track these deadlines, and HMRC also sends automated reminders if you're registered online—making compliance much easier.
Corporation Tax deadlines for small businesses
If it’s a limited company, paying Corporation Tax isn’t optional – and knowing your deadlines is just as important as knowing your profit margins. HMRC expects you to stay on top of both your filing and your payment dates.
Your Corporation Tax payment is due nine months and one day after the end of your company’s accounting period. For example, if your year-end is 31 March 2025, your Corporation Tax payment must reach HMRC by 1 January 2026. It’s worth noting that this deadline comes before your tax return is due, so you need to work out your liability ahead of time.
Filing your Company Tax Return (CT600) is a separate step, and the deadline for that is 12 months after your accounting period ends. Using the same example, a 31 March 2025 year-end means your return must be filed by 31 March 2026.
HMRC charges interest on late payments and can issue penalties for late filing, so it’s good practice to prepare your accounts early and get a clear picture of what you owe. This way, there are no surprises and no unnecessary fines.
Corporation Tax deadlines for small businesses
VAT Return and PAYE/National Insurance Deadlines
For many small businesses, staying on top of VAT and payroll obligations, both have clear deadlines, and missing them can quickly lead to fines or interest charges.
VAT returns are usually quarterly. You’ll need to submit your return and pay any VAT due one month and seven days after the end of your VAT period.
For example, if your VAT quarter ends on 31 March 2026, your return and payment are due by 7 May 2026. Filing late or paying late can result in penalties, so it’s wise to mark these dates well in your calendar.
PAYE and National Insurance (NI) deadlines depend on how often you pay your employees. If you report and pay monthly, submissions and payments must reach HMRC by the 22nd of the following month (or the 19th if paying by post). Even if you run a very small team, these deadlines are strict, and errors can lead to automatic fines.
Keeping clear payroll records and a calendar of VAT due dates makes it easier to avoid last-minute scrambles. Many small businesses use accounting software to manage both VAT and PAYE, reducing the risk of missing a deadline.
Automating reminders and payments can save time and prevent costly mistakes.
It’s also worth noting that HMRC expects businesses to stay accurate and timely even if you’re busy running other aspects of your company. Small errors, like misreporting a VAT figure or forgetting a PAYE submission, can trigger penalties or interest, so having a system in place to double-check entries is key.
By combining careful record-keeping with a proactive approach, you can make sure both VAT and payroll obligations are handled smoothly, leaving you free to focus on growing your business rather than chasing paperwork.
Tips to stay on top of tax deadlines in 2025
Keeping track of tax deadlines doesn’t have to be stressful. A few practical steps can make a big difference:
Use a calendar or reminder system – Mark key dates for Self Assessment, Corporation Tax, VAT, and PAYE in your phone or planner. Set reminders a week or two in advance so you’re never caught off guard.
Keep your records up to date – Regularly updating accounts, invoices, and payroll records means less last-minute scrambling when deadlines arrive.
Automate payments where possible – Using accounting software or direct debit for VAT and PAYE can reduce the risk of late payments.
Plan for payments in advance – Know what you owe ahead of time so your cash flow isn’t disrupted by a tax bill arriving unexpectedly.
Seek professional advice – Even a quick check-in with an accountant can help ensure you haven’t missed anything, and give you peace of mind that everything is filed correctly.
A little planning now saves a lot of stress later. Staying organised and proactive with tax deadlines means you can focus on running and growing your business.
Tips to stay on top of tax deadlines
Conclusion
Every missed deadline costs you money, but every met deadline builds your credibility. Clients, employees, and even lenders take notice when your finances run smoothly. That kind of discipline creates trust, and trust is the foundation of long-term success.
So, take what you’ve learned today and put it into action:
Mark your deadlines.
Get the right tools.
Don’t hesitate to seek professional help when needed.
The more proactive you are, the more confident you’ll feel, and the less HMRC deadlines will control your year. Instead, you’ll be in control of them.
Thanks for reading!
Meet Lewis
Lewis is a professional accountant and the founder of Rhombus Accounting. He regularly shares his knowledge and best advice on his blog and other channels, such as LinkedIn.
Book a call today to learn more about what Lewis and Rhombus Accounting can do for you.
