Do I Need an Accountant to Calculate My Capital Gains

At Towerstone, we provide specialist capital gains accountancy services for people unsure about calculations. We have written this article to explain when professional help is useful, helping you make informed decisions.

In my experience, this is one of the most honest and sensible questions people ask when dealing with Capital Gains Tax. It usually comes from a place of wanting to do the right thing without overcomplicating matters or spending money unnecessarily. Some people assume accountants are only for complex situations. Others assume Capital Gains Tax is so technical that professional help is always mandatory.

In my opinion, the truth sits firmly in the middle.

You are not legally required to use an accountant to calculate your capital gains. Many people are perfectly capable of doing it themselves. However, whether you should do it yourself depends on your circumstances, the type of assets involved, the number of transactions, and your tolerance for risk and uncertainty.

In this article, I am going to explain when you genuinely can calculate your own capital gains with confidence, when I strongly believe professional help is worth it, and what I have seen go wrong when people assume they do not need advice. Everything here is based on real world UK experience, not theory.

The Starting Point: Are You Allowed to Do It Yourself?

Let us be very clear from the outset.

You do not need an accountant to calculate your capital gains. There is no legal requirement to use one. HMRC expects individuals to be able to complete their own tax returns where appropriate.

HMRC does not care who calculates your Capital Gains Tax. It cares whether the calculation is correct, reasonable, and properly reported.

In my experience, HMRC will hold you responsible for errors regardless of whether you used an accountant or not.

Why People Ask This Question in the First Place

Most people ask whether they need an accountant because something about their situation feels uncertain.

Common triggers include:

• Selling a property
• Selling shares or investments
• Disposing of cryptocurrency
• Receiving an unexpected gain
• Being close to tax thresholds

In my opinion, that feeling of uncertainty is worth paying attention to. It does not automatically mean you need an accountant, but it does mean you should slow down and assess the situation properly.

Capital Gains Tax Is Procedural Not Mathematical

One of the biggest misconceptions I see is the idea that Capital Gains Tax is difficult because the maths is hard.

In my experience, the maths is usually straightforward. The difficulty lies in:

• Identifying all taxable disposals
• Applying the correct rules in the right order
• Understanding what counts as a gain or loss
• Knowing which reliefs apply and which do not

In my opinion, people who struggle with Capital Gains Tax usually struggle with interpretation rather than calculation.

Situations Where You Can Usually Do It Yourself

There are many situations where calculating your own capital gains is entirely reasonable.

From experience, you can often do it yourself if:

• You sold a single asset
• The transaction history is short and clear
• There are no complex reliefs involved
• You have good records
• You are comfortable following HMRC guidance

Let me expand on these in practical terms.

Selling a Single Asset With Clear Records

If you sold one asset such as a small shareholding or a straightforward investment and you have clear records of:

• Purchase price
• Sale price
• Fees paid

Then calculating the gain is usually very manageable.

In my experience, many people successfully handle these cases without professional help.

Gains Fully Covered by the Allowance

If your total capital gains for the year are clearly below the annual allowance and you are not required to report disposals, the risk is low.

That said, reporting requirements can still apply in some cases, which people often overlook.

In my opinion, even when no tax is payable, accuracy still matters.

Simple Share Sales Outside ISAs

Selling shares held outside an ISA with a small number of transactions is another situation where self calculation is often fine.

As long as you understand pooling rules and matching rules, this can be done carefully with HMRC guidance.

From experience, problems arise when people assume each share purchase stands alone rather than being pooled.

When Capital Gains Tax Starts to Get Risky

There are certain scenarios where calculating your own capital gains becomes significantly more risky.

This does not mean it is impossible. It means the cost of getting it wrong increases sharply.

In my opinion, these are the situations where professional help starts to make sense.

Property Sales Are a Major Risk Area

Property is one of the biggest areas where I see mistakes.

Capital Gains Tax on property involves:

• Private Residence Relief
• Periods of occupation and non occupation
• Letting considerations
• Changes in use
• Separate reporting deadlines

In my experience, people often assume their home is fully exempt when it is not, or they miss reliefs they were entitled to.

The sums involved are usually large, which magnifies the consequences of errors.

Multiple Transactions in One Tax Year

If you have made several disposals in a single tax year, the complexity increases.

This includes:

• Multiple share sales
• Multiple crypto disposals
• Rebalancing investment portfolios

From experience, it is very easy to miss a transaction or misapply losses when volume increases.

In my opinion, volume alone is a strong reason to consider help.

Cryptocurrency and Capital Gains Tax

Crypto is one of the biggest drivers of CGT errors.

From experience, people often:

• Miss crypto to crypto swaps
• Forget to value transactions in GBP
• Misunderstand pooling rules
• Ignore fees
• Underestimate the number of disposals

Even technically capable individuals often struggle with crypto CGT because the record keeping burden is so high.

In my opinion, crypto is an area where professional input often pays for itself.

Business Assets and Shares in Private Companies

If you are dealing with:

• Shares in private companies
• Business disposals
• Entrepreneurs’ Relief or similar
• Asset transfers connected to a business

Then I strongly believe professional advice is sensible.

These areas involve judgement calls, elections, and relief conditions that are easy to misunderstand.

From experience, mistakes here can cost tens of thousands of pounds.

Situations Involving Losses

Losses can reduce your tax bill significantly, but only if they are identified and used correctly.

From experience, people often:

• Forget to claim losses
• Claim losses incorrectly
• Miss time limits
• Apply losses in the wrong order

In my opinion, losses are one of the most underused and misunderstood parts of Capital Gains Tax.

Interaction With Income Tax

Capital Gains Tax does not sit in isolation.

Your income level affects:

• Which CGT rate applies
• How much of your gain is taxed at lower rates
• Whether planning opportunities exist

From experience, people often calculate CGT without factoring in their income, leading to surprises.

An accountant looks at the full picture rather than just the gain.

Reporting and Deadlines Catch People Out

Another reason people get into trouble is not calculation, but timing.

Capital Gains Tax has different reporting deadlines depending on the asset.

Property sales often have accelerated reporting requirements.

From experience, missing a deadline can trigger penalties even if the calculation itself was correct.

In my opinion, deadlines are an underrated risk.

HMRC Enquiries and Peace of Mind

One of the biggest benefits of using an accountant is not technical skill. It is confidence.

From experience, people who calculated their own CGT often worry later when they receive a letter or hear about HMRC enquiries.

An accountant provides:

• A documented methodology
• Clear workings
• Professional judgement

In my opinion, that peace of mind has real value.

What Happens If You Get It Wrong

HMRC does not penalise honest mistakes in the same way as deliberate errors, but mistakes still have consequences.

If you get your capital gains wrong, you may face:

• Additional tax
• Interest
• Penalties depending on behaviour

From experience, penalties are far more likely where HMRC believes reasonable care was not taken.

Using an accountant can help demonstrate reasonable care.

Can an Accountant Save You Money

This is a fair question.

In my experience, accountants often save clients more than they cost by:

• Identifying reliefs
• Using losses efficiently
• Planning timing of disposals
• Avoiding penalties

That said, not every situation leads to savings. Sometimes the calculation is straightforward and no planning is available.

In my opinion, the value lies in risk reduction as much as tax reduction.

When an Accountant Is Probably Not Necessary

To be balanced, there are cases where I genuinely believe an accountant is not necessary.

These include:

• A single small gain
• Clear records
• No property or crypto
• No complex reliefs
• Confidence in following guidance

In these cases, paying for professional help may not be proportionate.

Signs You Should Probably Speak to an Accountant

Based on experience, I would strongly suggest professional advice if:

• You feel unsure or anxious
• The sums involved are large
• You are dealing with property
• You are dealing with crypto
• You have many transactions
• You are close to thresholds
• You have had HMRC contact

In my opinion, uncertainty itself is a valid reason to seek help.

DIY With a Safety Net

One approach I often recommend is a hybrid.

You calculate your capital gains yourself, then ask an accountant to review the figures before submission.

This can:

• Reduce cost
• Catch errors
• Provide reassurance

From experience, this works well for people who are confident but cautious.

The Cost Versus Risk Calculation

Ultimately, this decision comes down to a cost versus risk calculation.

Ask yourself:

• How much tax is involved
• How confident am I in the rules
• How costly would an error be
• How much stress am I carrying

In my opinion, people often underestimate the emotional cost of uncertainty.

My Professional View

In my experience, most people are capable of calculating simple capital gains. Fewer people are capable of knowing when their situation is no longer simple.

That is the real skill.

I do not believe everyone needs an accountant for Capital Gains Tax. I do believe that many people who skip advice regret it later when mistakes come to light or when HMRC asks questions.

In my opinion, using an accountant is not about ability. It is about judgement.

Where this leaves you

So, do you need an accountant to calculate your capital gains?

Legally, no. Practically, sometimes yes.

If your situation is simple, well documented, and you are confident in the rules, doing it yourself can be perfectly reasonable.

If your situation involves property, crypto, multiple transactions, large sums, or uncertainty, professional help is often a sensible investment rather than a cost.

In my experience, the biggest mistakes happen not because people tried to do it themselves, but because they did not realise how complex their situation had become.

In my opinion, the safest approach is not to ask whether you can do it yourself, but whether you should.

If you would like to explore related Capital Gains Tax guidance, you may find Do I need to pay Capital Gains Tax on a gifted car or jewellery and How can an accountant help me plan ahead for Capital Gains Tax useful. For broader Capital Gains Tax guidance, visit our Capital Gains Tax hub.