Does HMRC Know About Your Side Income?

If I asked you to list every way you made money during the last tax year, could you?

Your salary might be obvious.

But what about:

• Interest on your savings?

• Rent from a property?

• Freelance work alongside your main job?

• Money from a side hustle?

• Dividends or investments?

• Income earned through an online platform?

• Something that started as a hobby but is now making money?

It’s increasingly common to have income coming from several different places.

The problem is that we tend to think about each one separately.

HMRC doesn’t necessarily see it that way.

And as HMRC gets better at receiving and matching information from different sources, it’s becoming increasingly important that you know what income you’ve received and whether you need to declare it.

What Income Does HMRC Know About?

Probably more than many people realise.

Some income is reported to HMRC automatically.

For example, if you’re employed, HMRC receives information about your pay and tax through PAYE.

Banks and building societies provide HMRC with information about savings interest.

Digital platforms can also have reporting obligations. This means information about people earning money through certain online platforms may be collected and reported to HMRC.

That could include platforms used for things such as selling goods, providing services or renting out property.

This doesn’t mean every pound reported by a platform is automatically taxable.

But it does mean relying on “HMRC won’t know about it” is becoming an increasingly risky approach.

HMRC Is Getting Better at Joining the Dots

Over the last few years, HMRC has been increasingly focused on closing the tax gap around side hustles, property income and other additional income.

If you earn money through platforms such as Airbnb, information about your activity may already be shared with HMRC.

With Making Tax Digital and huge advances in AI and data matching, HMRC will only get better at joining the dots — matching information from third parties to individual taxpayers and using it to prompt people or identify where something doesn’t look right.

The message is simple:

Know what income you’ve received, because there’s a good chance HMRC does too.

What Extra Income Might You Need to Declare?

A useful starting point is to forget about tax for a moment and simply make a list of where your money came from.

I’d break it down into five areas.

1. Employment and pension income

Start with salary, bonuses, taxable benefits and pension income.

Much of this may already be dealt with through PAYE, but it still forms part of your overall tax position.

2. Business, freelance and side-hustle income

Think beyond a traditional business.

Perhaps you:

• do occasional freelance work

• provide consultancy

• sell products

• make money from content

• provide services through an online platform

• have turned a hobby into something that generates income

You don’t necessarily need premises, employees or even think of yourself as a business owner for the tax rules to become relevant.

3. Property income

This could include income from:

• a rental property

• short-term or holiday accommodation

• renting out a room

• other property arrangements

If you have property income alongside a salary or business, it’s particularly easy to think of it as a completely separate pot of money.

For tax purposes, you need to understand the complete picture.

4. Savings and investments

Don’t forget income generated by your money itself.

This could include savings interest, dividends and other investment income.

Whether additional tax is due will depend on the type and amount of income and your individual circumstances.

5. Other income

Finally, ask:

“Have I received any other money that doesn’t fit neatly into those categories?”

Foreign income, commission, casual earnings and other sources of additional income can all be worth checking.

The aim isn’t to find reasons to pay more tax.

It’s to make sure you understand your own position before HMRC asks questions about it.

Does All Extra Income Have to Be Declared?

No, and this is an important distinction.

Receiving extra money does not automatically mean you have extra tax to pay.

There are various allowances and exemptions within the tax system.

For example, qualifying individuals may be able to use the £1,000 trading allowance for certain trading income, and there is a separate £1,000 property allowance for certain property income.

Likewise, selling your own unwanted belongings online does not automatically make you a trader.

Someone clearing old clothes from their wardrobe is very different from someone regularly buying products specifically to sell them for a profit.

The circumstances matter.

That’s why the better question isn’t:

“I received some extra money, do I owe tax?”

It’s:

“What was the money for, how much did I receive and do I need to tell HMRC about it?”

Try a 10-Minute Income Check

This is the practical exercise I’d recommend.

Take a piece of paper and write:

Employment | Business | Property | Savings & Investments | Other

Then look back over the tax year.

Check your bank accounts, savings accounts, online platforms and any other records you have.

Write down each source of income.

Don’t worry about calculating the tax yet.

Your first job is simply to create the complete picture.

Once you’ve done that, ask four questions about anything you’re unsure of:

1. Is this income taxable?

2. Is there an allowance or exemption that applies?

3. Does HMRC already have this information?

4. Do I need to do anything to report it?

If you can’t answer one of those questions, that’s the point at which it’s worth checking HMRC’s guidance or speaking to an accountant.

Don’t Forget the Self Assessment Registration Deadline

If your circumstances mean you need to complete a Self Assessment tax return and you haven’t previously registered, 5 October following the end of the relevant tax year is an important date to know.

For income received during the 2025/26 tax year, that means 5 October 2026.

You might need to consider Self Assessment if, for example, you’ve started working for yourself or have untaxed income that needs reporting.

However, don’t assume that having any additional income automatically means you need to submit a tax return. Your circumstances and the type and amount of income matter.

If you’re unsure, check before the deadline rather than waiting for HMRC to contact you.

Don’t Rely on HMRC to Spot Everything for You

There’s an interesting contradiction here.

HMRC has access to increasing amounts of financial information.

But that doesn’t mean you can simply assume:

“If HMRC needs to know, they’ll tell me.”

Ultimately, you’re responsible for making sure your tax affairs are correct.

That’s why good records matter.

You don’t need an elaborate financial system.

But you should be able to answer a fairly basic question:

Where did my money come from?

If you know that, working out what needs declaring becomes much easier.

Know Your Income Before HMRC Asks

Having several sources of income isn’t unusual anymore.

You could be employed and have a side hustle.

Run a limited company and own a rental property.

Be retired and receive investment income.

Have a full-time job but occasionally freelance.

The tax system can feel complicated when those different pieces start overlapping.

You don’t need to understand every tax rule yourself.

Start by understanding your money.

Make a list of every way you’ve received income. Check anything you’re unsure about. And deal with anything that needs reporting before it becomes a problem.

Know what you’ve earned. Know what needs declaring. Stay one step ahead.

Need Help With Your Tax Return?

If you have income from different sources and aren’t sure what needs to go on your Self Assessment tax return, getting advice early can make the process much simpler.

Blackdown Accounting helps individuals, sole traders and business owners in Sidmouth and across East Devon with Self Assessment tax returns and year-end accounts, helping you understand what needs reporting and get everything completed accurately and on time.

If you need help getting your 2025/26 tax return sorted, get in touch with Blackdown Accounting.