Self-Assessment Deadlines 2026: What You Need to File and When
- jaygosal
- 2 days ago
- 5 min read
Updated: 12 hours ago
Let's talk about everyone's favourite topic: tax deadlines. (We can practically hear the collective groan from here.)
If you're self-employed, a landlord, or a company director in Derby, Coventry, or anywhere across the Midlands, Self-Assessment deadlines matter. Miss them, and you'll face penalties that sting – not to mention the stress of dealing with HMRC.
The good news? With the right preparation and a clear calendar, you can sail through tax season without the panic. Let's break down exactly what you need to know for the 2025/26 tax year
What are the Key Self-Assessment Deadlines for 2026?
Mark these dates in your calendar right now:
5 October 2025
Register for Self-Assessment (if you're new)
If you're completing your first Self-Assessment – maybe you've just started a business, become a landlord, or had taxable income over £100,000 – you must register by this date for the 2024/25 tax year.
Late registration? You'll face an automatic £100 penalty, even if you don't owe any tax.
31 October 2025
Paper tax return deadline
Still prefer pen and paper? Your completed Self-Assessment must reach HMRC by 31 October 2025. But honestly? Unless you enjoy queuing at the post office and worrying about lost mail, we'd recommend filing online.
30 December 2025
Online filing deadline if you want HMRC to collect tax through PAYE
If you owe less than £3,000 and want HMRC to collect it through your tax code (rather than paying a lump sum), file online by 30 December 2025. This only works if you're employed or receive a pension through PAYE.
31 January 2026
The big one: Online filing and payment deadline
This is the date most people know (and dread). By midnight on 31 January 2026:
✓ Your online Self-Assessment for 2024/25 must be submitted
✓ Any tax owed must be paid in full
✓ Your first payment on account for 2025/26 is due (if applicable)
Miss this deadline and penalties start immediately – £100 on 1 February, then daily penalties after 3 months.
31 July 2026
Second payment on account
If you made a payment on account in January, your second instalment is due by 31 July 2026. This prepays your estimated tax bill for the 2025/26 tax year.
Who Needs to File Self-Assessment?
Not everyone needs to complete a tax return. You'll need to file if you're:
Self-employed with profits over £1,000
A landlord with rental income over £1,000
A company director (extracting dividends from their own limited company)
Receiving untaxed income like dividends over £500 or savings interest over £1,000
Claiming Child Benefit and your income exceeds £60,000
HMRC usually sends you a notice if they think you need to file, but it's your responsibility to check. Ignorance isn't a defence against penalties.
What You Actually Need to File:
Here's what HMRC wants to know about:
Income sources:
Employment income (if not taxed correctly)
Self-employment profits
Rental income from properties
Dividends from shares or company ownership
Savings interest
Foreign income
Capital gains from selling assets
Expenses and reliefs:
Business expenses (if self-employed)
Rental property expenses (if a landlord)
Pension contributions
Charitable donations
Marriage allowance transfers
Supporting information:
National Insurance number
UTR (Unique Taxpayer Reference) number
Records of all income and expenses
P60 from employers (if applicable)
P11D showing benefits in kind
Derby and Coventry business owners often ask us: "What records do I actually need?" The answer? Everything. Bank statements, receipts, invoices, mileage logs – keep it all for at least 6 years.
The Real Cost of Missing Deadlines:
Let's be blunt about HMRC penalties:
Miss 31 January deadline:
Immediate £100 fine (even if you owe no tax)
After 3 months: £10 daily penalties (up to £900)
After 6 months: 5% of tax owed or £300 (whichever is higher)
After 12 months: Another 5% of tax owed or £300
Late payment penalties:
30 days late: 5% of unpaid tax
6 months late: Another 5%
12 months late: Yet another 5%
Plus, interest charges on unpaid tax at currently around 7-8% annually.
One of our Coventry clients once said: "I put off filing for three months. The penalties cost me more than my actual tax bill." Don't be that person.
Common Self-Assessment Mistakes to Avoid:
We see these trip up even experienced business owners:
1. Leaving it until 30 January Why do this to yourself? File early and sleep easy. Plus, if there's an issue, you'll have time to fix it.
2. Forgetting about payments on account Many people budget for their January payment but forget July's instalment. Budget for both.
3. Not keeping proper records "I'll remember what that expense was for" – famous last words. Keep contemporaneous records and receipts.
4. Missing allowable expenses Self-employed people often miss legitimate business expenses. Every £1,000 in missed expenses costs you £200-450 in unnecessary tax.
5. Not declaring all income HMRC receives data from banks, employers, and property platforms. They'll know if you've missed something. Always declare everything.
How AccountingBliss Takes the Stress Out of Self-Assessment
Here's what we hear most often from Midlands business owners: "I just want someone to handle it so I can stop worrying."
We get it. Self-Assessment takes time you don't have, and one mistake can cost you hundreds in penalties.
Here's how we help:
Review all your income and expenses to ensure nothing's missed
Claim every allowable deduction to minimise your tax bill
Complete and file your return accurately and on time
Calculate your tax liability so there are no surprises
Send you deadline reminders for both filing and payments
Handle HMRC queries if any questions come up
Most importantly? You'll have peace of mind knowing it's done right.
Don't Wait Until January
The biggest mistake we see is people leaving Self-Assessment until the week before the deadline. Accountants are swamped in late January, you're stressed, and there's no time to optimise your tax position.
Start now. Get your records together, gather your paperwork, and either file early or book your accountant before the rush.
Ready to Make Self-Assessment Simple?
If you're a Derby or Coventry business owner or landlord who'd rather focus on earning money than wrestling with tax returns, we're here to help.
We offer a free 30-minute consultation to review your situation and show you exactly how we can take Self-Assessment off your plate.
Get in touch:
📞 Derby: 01332 577 289
📞 Coventry: 02475 098 680
Stop dreading Self-Assessment deadlines. Let us worry about the dates, the forms and the compliance, you just focus on building your financial freedom.
About AccountingBliss: We're Derby and Coventry-based accountants who help small business owners, landlords, and company directors handle Self-Assessment with confidence. We explain things clearly, respond quickly, and genuinely care about keeping more money in your pocket.
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