Tax return mistakes are easy to make when you are dealing with unfamiliar rules, missing information and a deadline at the same time.

Some mistakes mean you pay too little and have to correct the position later. Others mean you pay more tax than necessary because you forgot a valid claim or relief.

In this episode, we look at five areas that regularly cause problems: student loans, the High Income Child Benefit Charge, self-employed expenses, working from home and Gift Aid.

About this episode

Preparing your own tax return can feel daunting.

You are bringing together different sources of income, expenses, deductions and personal information, often using terminology you may only see once a year.

So forgetting something is not unusual.

These tax return mistakes usually happen because something has been overlooked, misunderstood or based on rules that have since changed.

The important thing is to understand the areas that commonly get missed and check them before you submit.

If you need the wider foundation first, see our guide to Self Assessment tax returns.

Mistake 1: Forgetting your student loan

If you have a student or postgraduate loan, do not assume that PAYE has automatically dealt with everything.

If you complete a Self Assessment return and your repayments are due, the student loan information forms part of that calculation.

The current system includes Plan 1, Plan 2, Plan 4, Plan 5 and Postgraduate Loans.

Yes, there still is no Plan 3.

The repayment threshold depends on the plan you are on, and those thresholds can change between tax years.

If you are self-employed, HMRC calculates the repayment through Self Assessment using your annual income.

If you are both employed and self-employed, repayments already taken through PAYE are taken into account when HMRC calculates what remains due.

So check which plan you are on and make sure the student loan section of the return is correct.

Mistake 2: Missing the High Income Child Benefit Charge

The High Income Child Benefit Charge is another area that can easily get overlooked.

It can apply where you or your partner receive Child Benefit and one of you has adjusted net income above the relevant threshold.

For tax years from 2024/25 onwards, the charge starts when adjusted net income is over £60,000.

Once adjusted net income reaches £80,000, the charge is equivalent to the full amount of Child Benefit received.

If both partners are above the threshold, responsibility normally falls on the partner with the higher adjusted net income.

It is adjusted net income that matters, not simply your headline salary or business turnover.

If you are dealing with the charge through Self Assessment, make sure the relevant information has not been left out.

Mistake 3: Missing allowable self-employed expenses

Paying tax on more profit than necessary is also a mistake.

If you are self-employed, allowable business expenses reduce the profit on which your tax calculation is based.

Typical costs may include things such as software, professional fees, advertising, business travel, office costs and other expenses connected with running the business.

However, do not fall into the opposite trap and assume that anything vaguely connected with work can automatically be claimed.

If a cost has both business and personal use, you can generally claim only the business element.

For example, if you use your mobile phone for both personal and business calls, you need a reasonable way to identify the business proportion.

Good bookkeeping makes this much easier because you are not trying to reconstruct twelve months of spending when the tax return deadline arrives.

This is a good example of why tax return mistakes can work both ways. You can underpay tax by leaving something out, but you can also overpay by failing to claim expenses you are entitled to.

Mistake 4: Using outdated working-from-home rules

This area has changed significantly since the original episode was recorded.

The old COVID-era working-from-home rules should not simply be carried forward into a current tax return.

From 6 April 2026, employees cannot claim tax relief for working-from-home expenses for the 2026/27 tax year.

Claims for some earlier tax years may still be possible if you met the rules that applied at the time.

The position is different if you are self-employed.

Self-employed people may still be able to claim the business proportion of eligible household costs when working from home.

Depending on your circumstances, you may calculate the actual business cost or use simplified expenses.

The key point is to apply the rules that match both your employment status and the tax year concerned.

Mistake 5: Getting Gift Aid wrong

Gift Aid can affect your tax position in more than one way.

When you make an eligible Gift Aid donation, the charity can normally reclaim basic-rate tax on that donation.

If you are a higher-rate taxpayer, you may also be able to claim additional tax relief through Self Assessment.

But there is another side to the rule.

You need to have paid enough Income Tax or Capital Gains Tax to cover the tax that the charity reclaims through Gift Aid.

If the charity claims more tax than you have paid, HMRC may ask you to make up the difference.

So do not simply tick the Gift Aid box and forget about it.

Keep a record of your donations and make sure the tax position supports the declaration you made.

The five tax return mistakes above cover very different parts of Self Assessment, which is why a final review before submission matters.

What if you have already filed and spotted a mistake?

Finding a mistake after filing does not automatically mean disaster.

You can normally amend a Self Assessment return within 12 months of the filing deadline.

If that amendment window has passed, different rules apply depending on whether you have underpaid or overpaid tax.

For example, overpayment relief may be available for up to four years after the end of the relevant tax year.

The important thing is to deal with the mistake once you become aware of it rather than hoping it disappears.

How to Avoid Common Tax Return Mistakes

Check your student loan position. Confirm the plan and any repayments already deducted.
Review Child Benefit. Check whether the High Income Child Benefit Charge applies.
Review your business expenses. Make sure you have included allowable costs without claiming personal spending.
Check working-from-home rules for the correct tax year. Do not rely on old COVID-era guidance.
Review Gift Aid donations. Check both the relief available and whether you paid enough tax to support the declaration.
Read through the completed return. Look for missing income, unexpected figures and anything that does not make sense.

A few extra minutes checking the return can save a lot more time later.

FAQs

What are common tax return mistakes?

Common tax return mistakes include forgetting student loans, missing the High Income Child Benefit Charge, overlooking allowable expenses, applying outdated working-from-home rules and failing to deal with Gift Aid correctly.

Do I include my student loan on Self Assessment?

If you are due to make student or postgraduate loan repayments and complete a Self Assessment return, the relevant loan information needs to be included so HMRC can calculate the repayment correctly.

Can I claim all my business expenses?

No. You can claim allowable business expenses. If a cost has both personal and business use, you generally claim only the business part.

Can employees still claim £6 a week for working from home?

Not for the 2026/27 tax year. From 6 April 2026, employees cannot claim working-from-home tax relief for the current tax year. Earlier eligible tax years are subject to the rules that applied at the time.

Can Gift Aid reduce my tax bill?

If you pay tax above the basic rate, Gift Aid donations may allow you to claim additional relief. You must also have paid enough Income Tax or Capital Gains Tax to cover the amount reclaimed by the charity.

Can I correct a Self Assessment tax return after submitting it?

Yes. You can normally amend the return within 12 months of the Self Assessment filing deadline. Other routes may be available after that period depending on the type of correction required.

Episode Timecodes

00:00 – Five common tax return mistakes
01:08 – Mistake 1: student loans
03:12 – Mistake 2: High Income Child Benefit Charge
04:39 – Mistake 3: self-employed expenses
05:21 – Mistake 4: working-from-home expenses
06:03 – Mistake 5: Gift Aid
07:12 – Five areas to check before submitting

Related episodes and guides

Key takeaway

Most tax return mistakes are easier to fix before you press submit.

Check the areas that are easy to forget, especially student loans, Child Benefit, business expenses, working-from-home costs and Gift Aid.

Do not rely on tax rules you remember from several years ago. Thresholds, reliefs and reporting requirements change.

Use good records, review the numbers and ask questions when something does not look right.

Getting the return correct is not about becoming a tax expert.

It is about knowing where the common traps are and checking them before they become a problem.

Plan it, Do it, Profit.

Further Support

If you want help understanding your tax, profit and other business numbers, use our free online business calculators.

If you need help reviewing your Self Assessment, correcting a tax return or understanding what you need to declare, you can contact us for an initial chat.

You can also watch more practical finance and tax support on the I Hate Numbers YouTube channel, or listen and follow on Apple Podcasts.

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5 Tax Return Mistakes to Avoid in Self Assessment