Investors are at risk of tax fines due to the HMRC Capital Gains Tax Glitch

A government system error could leave thousands of UK investors facing unexpected tax penalties this year. The problem stems from the HMRC Capital Gains Tax glitch, where online self-assessment forms are showing incorrect CGT figures. HMRC failed to correctly update its online tools after introducing rate changes in late 2024. Many investors using the portal have unknowingly submitted returns with inaccurate tax calculations.

This issue has already resulted in tax fines for investors, even when the mistake was caused by HMRC’s systems. Despite the glitch, HMRC continues to hold individuals accountable for any underpayment or omission.

In this article, we elucidate the issues, identify the individuals impacted, and suggest the appropriate course of action. We also outline how Apex Accountants can help you submit an accurate return, avoid penalties, and protect your financial position.

What Is the HMRC Capital Gains Tax Glitch?

The issue began after HMRC made updates following CGT rate changes announced in late 2024. However, technical errors mean some self-assessment forms are showing incorrect CGT calculations.

The main problems include:

• Incorrect CGT liabilities showing on some tax returns
  
• Errors in auto-filled figures within HMRC’s online forms
  
• Risk of underpayment or overpayment
  
• Potential late filing penalties due to delayed corrections
  

HMRC has acknowledged the issue, but many forms remain unfixed. The longer it remains unresolved, the higher the risk of HMRC penalties for capital gains submitted in error.

Who Is at Risk?

This issue may impact:

• Individual investors disposing of property, shares, or crypto
  
• Taxpayers using HMRC’s online self-assessment portal
  
• Anyone filing for the 2024–25 tax year without a manual review
  
• People relying on HMRC’s CGT calculator without professional checks
  

Even if the return is submitted on time, HMRC may still issue tax fines for investors who underreport gains due to faulty system outputs.

Key Risks to Investors

Here’s how the glitch could affect you:

• Incorrect CGT bills
  
• Interest and penalties on unpaid tax
  
• Compliance checks triggered by mismatches
  
• Time-consuming amendments and resubmissions
  
• Missed reliefs or incorrect loss reporting
  

Even small errors can result in significant HMRC penalties for capital gains, especially if not corrected before the deadline.

What You Should Do

To protect yourself, follow these steps:

• Check CGT figures manually using current tax rates
  
• Review disposal dates, purchase costs, and reliefs used
  
• Use updated software or a professional tax adviser
  
• Amend any already submitted return if it contains errors
  
• Keep accurate records for all disposals and gains
  

Submitting a correct return remains your responsibility—even if HMRC tools are faulty.

Why Choose Apex Accountants

At Apex Accountants, we specialise in helping investors file accurate, compliant tax returns—even when HMRC systems fall short. Our team knows what it takes to navigate Capital Gains Tax, and we work with individuals, landlords, and high-net-worth clients across the UK to reduce the risk of fines, penalties, and unwanted HMRC enquiries.

We don’t just process numbers—we help you make sense of them. Whether you’re reporting share disposals, crypto transactions, or second home sales, we provide practical, hands-on support at every stage of your tax journey.

Here’s how we help:

• Accurate Capital Gains Tax Reviews
  We calculate gains and losses correctly using up-to-date rates and identify all eligible reliefs, including Private Residence Relief and Business Asset Disposal Relief.
  
• Self-Assessment Filing with Confidence
  We prepare and submit your return on your behalf, review for HMRC system errors, and keep you informed throughout the process.
  
• HMRC Dispute Support
  From investigating miscalculations to appealing unfair penalties, we represent you with full technical support and clear communication.
  
• Specialist Advice for Property and Crypto Investors
  We provide tax guidance tailored to those dealing with residential property gains or complex digital asset portfolios.
  
• Digital Filing and MTD Compliance
  Our team helps you comply with Making Tax Digital and stay ahead of HMRC’s evolving digital requirements.
  

With Apex Accountants, you benefit from deep technical expertise, clear communication, and a responsive service built around your needs. Our advice is proactive, our support is ongoing, and our aim is always to protect your financial interests.

Speak to us today to get expert support with your Capital Gains Tax and investment reporting.

FAQs 

What caused the HMRC glitch?
The glitch occurred after CGT changes were introduced but not properly applied in HMRC’s online forms.

Who is affected by the error?
Anyone using HMRC’s self-assessment portal to report capital gains for the 2024–25 tax year may be at risk.

Can I fix a return if I’ve already submitted it?
Yes. You can file an amended return within the correction window or request a review if penalties are charged.

Will HMRC waive fines if it’s their fault?
Not automatically. You are still responsible for accurate returns. You may need to appeal any fine.

How do I check if my figures are wrong?
Compare your CGT calculations manually or consult a qualified accountant for review.

Is this glitch affecting crypto investors?
Yes. Reporting capital gains from digital assets through HMRC’s online tools also impacts them.

Can I claim CGT losses during this period?
Yes, provided the losses are recorded and submitted correctly. These can offset gains and reduce liability.

When is the self-assessment deadline?
For the 2024–25 tax year, the deadline is 31 January 2026.

Is the problem ongoing?
HMRC is working on fixes, but as of January 2026, many users still report incorrect calculations.

Should I still use HMRC’s portal?
Yes, but verify all figures carefully. You may also consider using an agent or external software.