Self-Assessment Tax Return Deadline 2025/26: Everything You Need to Know

CATEGORY: Tax Deadlines | Posted: December 2024 | Updated: December 2024

Don't miss the deadline! Learn about key dates, penalties, and how to file your self-assessment tax return on time for the 2024/25 tax year. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━Key Dates at a Glance

• 5 April 2025: End of 2024/25 tax year

• 5 October 2025: Deadline to register for self-assessment (if new)

• 31 October 2025: Paper return deadline

• 31 January 2026: Online filing deadline AND payment deadline

• 31 January 2026: First payment on account due (if applicable)

• 31 July 2026: Second payment on account due (if applicable)

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Who Needs to File a Self-Assessment Tax Return?

You must file a self-assessment tax return if you're:

Self-Employed or a Sole Trader

If you earned more than £1,000 from self-employment in the 2024/25 tax year, you need to register and file a return. This includes freelancers, contractors, consultants, and small business owners.

Company Directors

All company directors must complete a self-assessment, even if you only take a small salary or dividends from your company.

High Earners

If you earn over £100,000 per year from employment, you need to file even if you have no other income. This is because you start losing your personal allowance above this threshold.

Rental Income

Landlords with rental income over £1,000 (after allowable expenses) must file a return. This includes both residential and commercial properties.

Other Income Sources

You'll also need to file if you have:

• Capital gains over £3,000 (£6,000 for 2024/25)

• Savings or investment income over £10,000

• Foreign income

• Income from trusts or settlements

Not Sure If You Need to File?

HMRC may send you a notice to file, but don't wait for this. If any of the above apply to you, it's your responsibility to register and file on time.

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Penalties for Late Filing - Don't Risk It

HMRC penalties escalate quickly, so it's crucial to file on time:

Immediate Penalties

• 1 day late: £100 automatic penalty (even if you owe no tax)

• 3 months late: £10 per day (up to £900 maximum)

• 6 months late: £300 or 5% of tax due (whichever is higher)

• 12 months late: Another £300 or 5% of tax due

Plus Interest on Unpaid Tax

In addition to penalties, you'll pay interest on any unpaid tax from 31 January 2026 until you pay. The current rate is around 7.75% per year.

Example Cost of Being Late

If you owe £2,000 in tax and file 4 months late:

• Late filing penalty: £100

• Daily penalties (90 days): £900

• Late payment penalties: £100 (5% of £2,000)

• Interest charges: ~£50

• Total cost: £1,150 extra - plus your original £2,000 tax bill!

This is why filing on time is so important, even if you can't pay immediately. File the return to avoid the filing penalties, then arrange a payment plan with HMRC if needed.

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How to File Your Self-Assessment Tax Return

Step 1: Register for Self-Assessment (If New)

If this is your first time filing, you need to register with HMRC by 5 October 2025. They'll send you a Unique Taxpayer Reference (UTR) number, which can take up to 10 working days.

Step 2: Gather Your Information

You'll need:

• Your UTR and National Insurance number

• Records of all income (employment, self-employment, rental, dividends, interest)

• Details of any pension contributions

• Records of allowable expenses (if self-employed)

• Student loan information (if applicable)

• Information about any benefits or state support received

Step 3: Calculate Your Income and Expenses

For self-employed individuals, you need to calculate your profit:

• Total all business income

• Subtract allowable expenses (office costs, travel, equipment, etc.)

• The result is your taxable profit

Step 4: Complete the Return

You can file online through:

• HMRC's online portal (free)

• Commercial accounting software like Xero or Sage

• Through an accountant (we handle everything for you!)

Step 5: Pay What You Owe

Payment must reach HMRC by 31 January 2026. You can pay via:

• Online or telephone banking

• Direct Debit

• Debit or credit card online

• CHAPS (Clearing House Automated Payment System)

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Payment on Account - What You Need to Know

If you owe more than £1,000 in tax, you'll likely need to make "payments on account" - advance payments towards your next tax bill.

How It Works

Your total tax bill is split into three payments:

1. First payment on account: 31 January 2026 (50% of last year's bill)

2. Second payment on account: 31 July 2026 (remaining 50%)

3. Balancing payment: 31 January 2027 (any additional tax owed)

Example

If your 2024/25 tax bill is £3,000:

• 31 January 2026: Pay £1,500 (first payment on account for 2025/26)

• 31 January 2026: Also pay £3,000 (your actual 2024/25 bill)

• Total due 31 January 2026: £4,500

• 31 July 2026: Pay £1,500 (second payment on account)

This can be a shock if you're not prepared! Plan ahead and set aside money throughout the year.

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Common Mistakes to Avoid

1. Waiting Until the Last Minute

Don't leave it until 30 January! Technical issues, missing information, or questions from HMRC can cause delays. Aim to file by Christmas.

2. Not Claiming All Allowable Expenses

Self-employed? You can claim expenses like:

• Home office costs (simplified or actual)

• Business travel and mileage (45p per mile for first 10,000 miles)

• Professional fees and subscriptions

• Equipment and software

• Marketing and advertising

• Professional development and training

Many people miss hundreds of pounds in deductions!

3. Forgetting About Multiple Income Sources

Remember to include ALL income:

• Interest from savings

• Dividends from investments

• Rental income (even from Airbnb)

• Side hustles and freelance work

• Foreign income

4. Incorrect National Insurance Calculations

Class 2 and Class 4 National Insurance for self-employed individuals is often calculated incorrectly. This can lead to queries from HMRC or underpayment.

5. Not Keeping Proper Records

You must keep records for at least 5 years after the 31 January filing deadline. This includes:

• Invoices and receipts

• Bank statements

• Mileage logs

• Business expenses records

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Top Tips for Stress-Free Filing

Start Early Don't wait until January. Gather your information now and file in November or December when accountants are less busy.

Use Accounting Software Tools like Xero automatically track income and expenses throughout the year, making tax returns much easier.

Claim Every Deduction Review your expenses carefully. Even small amounts add up and reduce your tax bill.

Set Money Aside Put aside 25-30% of your self-employment income throughout the year to cover tax and National Insurance.

Consider Professional Help An accountant can:

• Ensure you claim all allowable expenses

• Identify tax-saving opportunities

• Handle the entire filing process

• Respond to HMRC queries on your behalf

• Save you time and stress

The cost of an accountant (£100-£200 for a basic return) is often less than the tax they save you!━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

What If You Can't Pay Your Tax Bill?

If you're struggling to pay your tax bill by 31 January, don't ignore it. HMRC offers several options:

Time to Pay Arrangement

You can spread your payment over up to 12 months if you:

• Owe less than £30,000

• Have no other payment plans or debts with HMRC

• Are up to date with your tax returns

Apply online through your HMRC account or call them directly. It's much better to arrange this than to miss the payment deadline and face penalties.

Budget Payment Plan

Set up a monthly Direct Debit to pay your next tax bill in advance. This spreads the cost throughout the year rather than one large payment.

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Key Takeaways

✓ File by 31 January 2026 to avoid automatic £100 penalty

✓ New to self-assessment? Register by 5 October 2025

✓ Keep detailed records of all income and expenses

✓ Don't forget payment on account if you owed over £1,000 last year

✓ Start gathering information now - don't wait until January!

✓ Consider using an accountant to maximize deductions and save time

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Need Help with Your Self-Assessment?

Don't let the deadline stress you out. At iUfinance, we handle self-assessment tax returns from just £100 for basic returns.

Our service includes:

✓ Complete preparation and filing of your return

✓ Identification of all allowable expenses and deductions

✓ Tax planning advice to minimize future bills

✓ HMRC correspondence handling

✓ Peace of mind that it's done correctly

We work with sole traders, landlords, contractors, and company directors across the UK.

Don't wait until January - contact us today and get it sorted early!━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━