How Do I Report Capital Gains Tax to HMRC

At Towerstone, we provide specialist capital gains accountancy services for individuals, landlords, and business owners. We have written this article to explain how and when Capital Gains Tax must be reported to HMRC, helping you make informed decisions.

This is one of those questions that people often ask far too late, usually after they have already sold an asset and then start to worry about deadlines, penalties, and whether they have done something wrong. From experience I can say that most Capital Gains Tax problems are not caused by the tax itself, but by confusion around how and when gains need to be reported to HMRC.

In my opinion reporting Capital Gains Tax is actually very logical once you understand the structure, but HMRC uses different reporting routes depending on what you have sold, when you sold it, and whether you are already within Self Assessment. That is where people get caught out.

In this guide I will explain in plain UK terms how to report Capital Gains Tax to HMRC, which forms and systems are used, when you must report, when you must pay, and how to avoid the most common mistakes I see in practice. Everything here is based on real world UK experience rather than theory.

The First Thing to Understand About Reporting Capital Gains Tax

The most important thing to understand is this.

Reporting Capital Gains Tax and paying Capital Gains Tax are not always the same thing, and they do not always happen at the same time.

From experience many people assume they only need to do something if tax is actually due. That is not always true. In some cases you must report a gain even if no tax is payable because allowances cover it.

HMRC cares about:

Whether a disposal has occurred

Whether it needs to be reported

Whether tax is due

Whether it has been paid on time

Each of those is assessed separately.

When You Need to Report Capital Gains Tax

You usually need to report Capital Gains Tax if:

You have disposed of an asset

The disposal is not fully covered by reliefs

The disposal meets HMRC reporting criteria

From experience the most common disposals that trigger reporting are:

Selling a buy to let or second property

Selling shares or investments outside an ISA

Selling or swapping cryptocurrency

Gifting assets to someone other than a spouse or civil partner

Selling business assets

Even if no tax is ultimately due, reporting may still be required.

The Two Main Ways to Report Capital Gains Tax

There are two main routes for reporting Capital Gains Tax to HMRC.

These are:

The Capital Gains Tax on UK Property service

Self Assessment tax returns

Which one you use depends primarily on the type of asset and your personal tax position.

From experience this distinction causes more confusion than anything else.

Reporting Capital Gains Tax on UK Property

If you dispose of UK residential property that is not fully exempt, you usually must report the gain using the UK Property Capital Gains Tax service.

This applies to:

Buy to let properties

Second homes

Holiday lets

Properties that were once your home but are no longer fully covered by main residence relief

Part disposals of residential property

The 60 Day Rule

One of the most important rules is the 60 day reporting and payment deadline.

You must usually:

Report the disposal within 60 days of completion

Pay any Capital Gains Tax due within the same 60 days

From experience people often assume exchange of contracts starts the clock. It does not. Completion is the key date.

Missing the 60 day deadline almost always results in penalties, even if no tax is ultimately due.

How to Report a Property Disposal Online

To report a property disposal you must use HMRC’s online Capital Gains Tax on UK Property service.

The process usually involves:

Creating or accessing a Government Gateway account

Logging into the Capital Gains Tax property service

Entering details of the disposal

Calculating the gain

Submitting the report

Paying any tax due

From experience this system is fairly user friendly, but it relies heavily on you having accurate figures.

What Information You Need for a Property Report

You will need to provide:

Property address

Date of acquisition

Date of completion

Purchase price

Sale price

Acquisition costs

Disposal costs

Periods of occupation

Reliefs claimed

Your income level to calculate the tax rate

In my opinion the biggest errors come from incorrect occupation details and misunderstanding main residence relief.

Do I Still Need to Include Property Gains on My Tax Return

Often yes.

If you are already within Self Assessment, the property gain still needs to be included on your Self Assessment tax return for the year.

The 60 day report does not replace the tax return. It is effectively a payment on account.

From experience people think the job is done after the 60 day report and then get confused when HMRC expects the gain to appear again later.

Reporting Capital Gains Tax Through Self Assessment

For most non property assets, Capital Gains Tax is reported through Self Assessment.

This applies to:

Shares and investments

Cryptocurrency

Business assets

Land that is not residential property

Gifts of assets

Most disposals outside property

If you are already registered for Self Assessment, gains are reported on the Capital Gains pages of your return.

If you are not registered, you may need to register.

When You Need to Register for Self Assessment

From experience you may need to register for Self Assessment if:

You have chargeable gains to report

You are not already filing tax returns

HMRC requires a return based on your circumstances

Registration deadlines matter. Late registration can cause knock on delays and penalties.

In my opinion it is always better to register early rather than wait until January.

What Information Goes on the Capital Gains Pages

The Capital Gains section of the tax return requires:

A summary of disposals

Total proceeds

Total allowable costs

Net gains or losses

Reliefs claimed

Losses brought forward or carried forward

You do not list every single transaction on the face of the return. HMRC expects you to keep detailed records and provide them if asked.

From experience the return is a summary, not a full transaction log.

When Capital Gains Tax Is Paid Through Self Assessment

For gains reported through Self Assessment, payment is usually due by 31 January following the end of the tax year.

For example:

Gains made in the 2024 to 2025 tax year

Reported on a tax return by 31 January 2026

Tax paid by the same date

From experience people often confuse reporting deadlines with payment deadlines.

Reporting Capital Gains Tax When No Tax Is Due

This is an area that surprises many people.

You may still need to report gains even if:

The gain is covered by the annual exempt amount

Losses reduce the gain to nil

Reliefs eliminate the tax

HMRC wants visibility of certain disposals, not just tax payments.

Failing to report when required can still result in penalties.

Reporting Capital Losses

Capital losses are just as important to report as gains.

From experience many people fail to report losses and then cannot use them later.

Losses must usually be reported to HMRC within four years of the end of the tax year in which they arose.

Once reported, losses can be carried forward indefinitely and offset against future gains.

Supporting Calculations and Records

Although HMRC does not require full calculations to be submitted with the return, you must have them.

From experience HMRC often asks for:

Calculation workings

Purchase and sale evidence

Valuations

Exchange rates used

Evidence of reliefs

In my opinion keeping clear supporting schedules alongside your return is essential.

Common Mistakes When Reporting Capital Gains Tax

Over the years I have seen the same mistakes repeatedly.

These include:

Missing the 60 day property deadline

Assuming no reporting is needed if no tax is due

Forgetting crypto to crypto disposals

Reporting gains but not losses

Using the wrong disposal date

Mixing up exchange and completion

Paying tax but failing to report properly

Reporting through the wrong system

In my opinion most of these errors come from misunderstanding process rather than tax law.

What Happens If You Report Late

If you report Capital Gains Tax late, HMRC can charge:

Late filing penalties

Late payment penalties

Interest on unpaid tax

Penalties can apply even if the tax itself is small.

From experience HMRC is far less forgiving on missed deadlines than on calculation errors that are corrected promptly.

Amending a Capital Gains Tax Report

If you make a mistake, it is usually possible to amend.

You can:

Amend a UK property report

Amend a Self Assessment return

Write to HMRC with corrections

From experience correcting errors early reduces penalties significantly.

Do I Need to Attach Evidence to My Return

Usually no.

HMRC does not require evidence to be submitted automatically.

However you must keep it and be ready to provide it if requested.

Submitting unnecessary evidence can slow things down rather than help.

Using an Accountant to Report Capital Gains Tax

From experience an accountant adds value by:

Confirming whether reporting is required

Choosing the correct reporting route

Calculating gains accurately

Applying reliefs correctly

Avoiding missed deadlines

Dealing with HMRC queries

In my opinion complex disposals should never be reported without at least some professional input.

How HMRC Checks Capital Gains Tax

HMRC uses multiple methods including:

Land Registry data

Exchange data

Information sharing

Cross checking tax returns

Targeted compliance campaigns

From experience Capital Gains Tax errors are often identified years later.

My Practical Advice From Experience

If I had to summarise reporting Capital Gains Tax in practical terms, my advice would be:

Identify disposals early

Work out whether property rules apply

Note deadlines immediately

Calculate gains carefully

Report even if no tax is due where required

Keep detailed records

Do not assume HMRC will tell you what to do

In my opinion proactive reporting avoids almost all problems.

Key Takeaways

So how do you report Capital Gains Tax to HMRC.

You report it either through the UK Property Capital Gains Tax service or through Self Assessment, depending on what you have sold. You report it based on the disposal date, not when you feel ready. You pay it based on strict deadlines, not convenience.

From experience the fear around Capital Gains Tax usually comes from uncertainty rather than cost. Once you understand the reporting routes and timing, the process becomes predictable and manageable.

If there is one message I would leave you with it is this. Capital Gains Tax is not something to react to after the event. It is something to plan for and report calmly, accurately, and on time. Doing that turns a stressful obligation into a routine part of managing your finances.

If you would like to explore related Capital Gains Tax guidance, you may find How does Capital Gains Tax apply to business asset disposals and How does Capital Gains Tax work on cryptocurrency and NFTs useful. For broader Capital Gains Tax guidance, visit our Capital Gains Tax hub.