Millions Face Unexpected Tax Bills Due to HMRC Tax Code Changes

Millions Face Unexpected Tax Bills Due to HMRC Tax Code Changes
Charlotte Baroukh

Charlotte Baroukh

Tax Expert @ Pie

3 min read

Updated: 28 May 2025

3 min read

Updated: 28 May 2025

Millions of UK taxpayers are facing unexpected tax bills due to changes in HMRC's tax code adjustments and increased scrutiny of side hustle income.


The combination of PAYE underpayments and undeclared earnings from secondary income sources has led to a surge in tax demands, catching many off guard. This article explores the reasons behind these unexpected bills, the demographics most affected, and how taxpayers can navigate the evolving landscape.

The Surge in Unexpected Tax Bills

HMRC has reported a significant increase in the number of taxpayers receiving unexpected tax bills. This surge is attributed to underpayments in the PAYE system and unreported income from side hustles.


The complexity of modern income streams, including gig economy jobs and online sales, has made it challenging for the traditional PAYE system to accurately capture all taxable income. Taxpayers are advised to review their tax codes and ensure all sources of income are accurately reported to avoid surprises.

PAYE Underpayments Explained

The PAYE (Pay As You Earn) system is designed to deduct income tax directly from salaries. However, it may not account for multiple income sources or changes in employment status, leading to underpayments. HMRC typically identifies these discrepancies at the end of the tax year and issues P800 tax calculations to inform taxpayers of any underpaid tax.

Side Hustles and the £1,000 Trading Allowance

The rise of the gig economy has led many individuals to earn additional income through side hustles. While the first £1,000 of such income is covered by the trading allowance and is tax-free, earnings above this threshold must be declared.


Failure to report this income can result in unexpected tax bills and potential penalties. HMRC plans to increase the reporting threshold to £3,000 by 2029, allowing more flexibility for side hustlers.

Delayed P800 Notifications

Typically, HMRC sends out P800 tax calculations by November. However, delays have been reported, with some taxpayers receiving notifications as late as March.


This delay can result in tax being deducted from April paychecks without prior notice, causing financial strain. Taxpayers are encouraged to proactively check their tax status and not rely solely on HMRC notifications.

The Role of Digital Platforms in Reporting Income

From January 2024, digital platforms like Airbnb, Uber, and Etsy are required to report user earnings directly to HMRC. This increased transparency aims to ensure all taxable income is accounted for. Individuals earning through these platforms should maintain accurate records and report income accordingly to avoid unexpected tax liabilities.

Expert Opinions and Recommendations

Tax experts recommend regular reviews of personal tax codes and proactive reporting of all income sources. Utilising HMRC's online tools and seeking professional advice can help navigate the complexities of modern tax obligations.


Staying informed and compliant is crucial in avoiding unexpected tax bills and ensuring financial stability.

Fun Fact

The UK's PAYE system was introduced in 1944 during World War II to simplify tax collection and ensure a steady flow of revenue for the war effort.


Over the decades, it has evolved to accommodate various income types, but the rise of the gig economy and digital platforms presents new challenges in tax administration.

Conclusion

Millions of UK taxpayers are facing unexpected tax bills due to underpayments in the PAYE system and unreported side hustle income. Understanding tax obligations and proactive reporting are essential in navigating these challenges.

Frequently Asked Questions

What is a P800 tax calculation?

A P800 is a tax calculation issued by HMRC when they believe you've paid too much or too little tax. It summarises your income and tax paid, highlighting any discrepancies.

How can I avoid unexpected tax bills from side hustles?

Ensure all additional income is reported to HMRC, especially if it exceeds the £1,000 trading allowance. Keep accurate records and consider consulting a tax professional.

What should I do if I receive a P800 late?

Review the calculation promptly, verify its accuracy, and contact HMRC with any concerns. Adjust your finances to accommodate any tax owed.

Are digital platform earnings taxable?

Yes, income from platforms like Airbnb, Uber, and Etsy is taxable and must be reported to HMRC, especially as these platforms now report user earnings directly.

Will the increase in the reporting threshold to £3,000 reduce my tax liability?

No, the increase affects reporting requirements, not tax liability. Income above £1,000 is still taxable; the change simplifies the reporting process for earnings between £1,000 and £3,000.

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