Self-assessment deadline stress? Don’t make these mistakes!

Blackberry-picking season is here and kids are back in school. This also means the deadline for filing your self-assessment tax return is approaching fast.

If you’re self-employed, you’re obliged to file a Form 11 tax return. If you’re a PAYE worker but have other income, the deadline applies to you, too, and you may need to submit a Form 11 or Form 12.

And for all taxpayers, by filing a tax return, it is possible to get a tax rebate on certain expenses, such as medical expenses, tuition fees, nursing home fees, or carer’s allowance.

This article outlines some trickier aspects of getting everything correct with the benefit of Rory Coll, principal partner at Galway-based Coll & Co – The Tax Specialists.

Here’s what we talk about:

1. Make sure you use the correct deadline

Revenue has now made online filing mandatory for most taxpayers, with very few exceptions.

So, in the main, the deadline to file and pay your tax return on ROS (Revenue Online Service) is Wednesday, 19 November 2025, but this only applies if both the tax return and payment are made through ROS.

This deadline is so widely discussed that people forget it’s not necessarily correct for everybody. It is, in fact, an extension of the earlier deadline of 31 October 2025, and this deadline still applies for some people.

An example would be if you pay by cheque or bank draft. That is, although you file your tax return online, you send your payment by post. Therefore, you must both file online and ensure that the cheque or bank draft reaches Revenue by 31 October 2025, with a postal receipt to prove it.

Also, one deadline has already passed but is worth bearing in mind for next year: if you file a paper tax return (Form 11) before 31 August, Revenue will complete the self-assessment section on your behalf.

2. Ensure you understand the tax system so don’t underpay

It is important to have a broad understanding of the tax system.

For example, even if you have an accountant to do your tax returns, you still need to understand your tax obligations in terms of income tax, PRSI (Pay Related Social Insurance) and Universal Social Charge (USC).

Understanding how these work and what they mean for your business will ensure you are compliant and minimise your tax liability.

Here’s a good example of why this matters. A potential slip-up for PAYE workers is not paying PRSI on their self-employed income portion. If you have a PAYE job where PRSI is deducted by your employer, you may still have to pay Class S PRSI on your self-employed income. This applies if your self-employed income is €5,000 or over.

3. Is your preliminary tax calculation correct?

The term “preliminary tax” can cause confusion, especially for those without a financial background.

In essence, your self-employed income tax liability can comprise two elements – the balance of income tax payable from 2024 and a preliminary tax liability for 2025.

Taxpayers are obliged to calculate and pay the current year’s (2025) liability at the time of submission/payment of their 2024 tax return.

As the final liability for 2025 will not become clear until year end, you mainly have two options. You can either:

1. Pay an amount equivalent to 100% of the total 2024 liability, or;
2. Pay an amount not less than 90% of the estimated 2025 tax liability. However, as 2025 is not yet complete, this may prove difficult to calculate.

Which you choose must mean your preliminary tax is equal to, or exceeds, the lowest of either of these.

Rather than risk underpaying the 2025 preliminary tax, it is advisable to choose the first option, as it provides more certainty and means you are less likely to be exposed to potential penalties from Revenue.

Then, in 2026, when you are paying your 2026 preliminary liability, you will also have to pay the outstanding amount of your 2025 tax liability.

Also, Rory stresses that Revenue is getting stricter and is increasingly charging interest when you submit your tax return and no preliminary tax has been paid. This interest is charged at a daily rate of 0.0219% per day.

There’s also a third option for preliminary tax that is sometimes used in an attempt to avoid penalties when your income (and therefore tax liability) has unfortunately fallen: you can pay 105% of the tax due for the year preceding the previous tax year (known as the “pre-preceding year”), providing this isn’t nil. You can only use this option if you pay by direct debit.

4. Is it time to use an accountant?

A key issue to consider is whether you should do your tax return yourself or hire an accountant to file on your behalf.

“If your finances include multiple income streams, capital allowances, or tax reliefs, professional help can often save more than it costs,” advises Rory.

And on the plus side, professional fees are also likely tax deductible.

As your business grows, not only does the complexity of its tax affairs grow but the time you can dedicate each year to the admin also might reduce. Therefore, employing an accountant is often seen as an effective cost-saving milestone for a growing business.

Whichever accountant you use, ensure they’re authorised with regard to ROS and that you provide them with the appropriate ROS authorisation. This might take a short while to setup, so ensure you do this ahead of deadlines.

5. Claim the correct expenses to potentially reduce your bill

For self-employed income, any expenses made for business purposes can be offset against your taxable income. In technical terms, expenses incurred wholly and exclusively for the purpose of the trade can generally be deducted from taxable profits.

This includes employees’ pay, rent, the purchase of goods for resale, utility bills, professional fees, interest on business loans, and other running costs.

In addition, when you purchase significant business assets like machinery, tools, equipment, or vehicles, you can claim capital allowances.

This allows you to write off the cost of the asset against your taxable profits over several years, typically at a rate of 12.5% per year for eight years. Also, in the case of most industrial buildings, it is 4% over 25 years.

If an expense incurred is both for business and personal use, then only the percentage that applies to the business may be claimed as a tax-deductible expense. An example would be mobile phone expenses, that may be used for both personal and business purposes.

Pre-trading expenses incurred before your business commenced, can be claimed. An example would be the cost of advertising or feasibility studies in relation to setting up your business.

If all this sounds overwhelming then that’s understandable. But avoid the instinct to just ignore it. Getting it right can make a huge difference to the amount of tax you pay.

Can you claim remote working relief?

A tax relief that has come to the fore in recent years is remote working relief, or working from home (WFH) relief. It was updated after the pandemic, though the relief claimable is still not significant.

If you work remotely or full-time at home, either as an employee or self-employed individual, you may be entitled to claim relief on certain home office expenses, including:

• Electricity
• Heating
• Broadband.

You can claim 30% of the relevant bills, apportioned for the number of days worked from home.

You then get tax relief on the amount of your costs at a rate of 20% or 40%, whichever is the highest rate of income tax you pay.

Also, if you are a PAYE remote worker, your employer can pay you up to €3.20 per day without deducting income tax, PRSI or USC. And if you claim Remote Working Relief on top of this, any remote working expenses paid by your employer must be deducted from your claim.

Rory says it is important to keep copies of your utility bills and a log of your WFH days for accurate apportionment.

However, he also has a word of caution, in particular about claiming for heat and electricity in excess of the 30% mentioned above. It may raise a red flag and lead to problems when you look to sell your house. While the possibility may be small, Rory has seen examples where Revenue has decided that the claiming of business expenses relating to home office use has impacted Principal Private Residence relief. This meant that the apportioned gain on sale was denied relief on the business-used portion, making it subject to Capital Gains Tax of 33%.

Can you claim business expenses applicable to employees?

In terms of PAYE employees, certain categories of workers can also claim flat rate expenses, such as nurses, shop assistants, plumbers.

In addition, all employees, including directors, can claim tax relief if they use the bus, Luas or train to get to work, with the company buying a Taxsaver Commuter Ticket Scheme ticket on the employee’s behalf.

Taxsaver Commuter Ticket Scheme tickets are not subject to tax, PRSI or USC. If the deduction is made from the employee’s pay, the employer’s PRSI can be reduced by up to 10.75%. Employees can also save between 28.5% and 52% of travel costs due to tax, PRSI and USC savings.

What about pension contributions?

A good way of cutting your tax bill is by making pension contributions.

“Pension contributions are one of the most effective and underused tax-saving tools available,” adds Rory.

Contributions to approved retirement schemes, such as PRSAs (Personal Retirement Savings Accounts) or personal pensions, are tax-deductible. Relief is granted at your marginal rate of tax, which is either 20% or 40%, depending on your income level. For example, every €1,000 contributed could reduce your tax bill by up to €400, if you’re in the higher tax bracket.

Also, as Rory points out, contributions made before 31 October 2025 (or mid-November if filing via ROS) can be backdated to 2024, reducing last year’s tax bill even after the tax year has ended.

You may have been hearing about My Future Fund on TV or similar. This applies only to PAYE employees, and isn’t relevant for self-employed workers, who it’s assumed make their own arrangements.

Can you claim for non-business expenses?

There are other non-business expenses that you can claim 20% tax relief on.

These include medical expenses, tuition fees and carer’s allowance.

Tax relief can be even higher for nursing home fees, at 40%, depending on your income.

Take care with your business expenses

So, there is significant potential to reduce your tax bill.

However, if you make any inaccurate declarations, such as failing to report all income sources, or incorrectly claiming non-business expenses, you could be penalised.

6. Ensure you keep adequate records

It is important to maintain records throughout the year in terms of invoices, receipts and business-related expenses.

If transactions are recorded regularly and accurately, it should expedite the preparation of the business accounts required to complete the tax return.

As Rory points out: “Poor records can lead to missed deductions and unnecessary stress at tax time.”

Using reputable accounting software such as Sage can simplify your record keeping and track income, invoices, expenses and also draw up financial statements.

You need to hold on to your supporting documents, too.

Revenue can ask to see your receipts, invoices and supporting documents for up to six years after the relevant tax year. This means that if you file your 2024 return in 2025, you should keep all related records (paper or digitally), until at least the end of 2031.

In addition, Rory advises retaining records for capital transactions e.g. land or buildings, including enhancements, indefinitely.

However, increasingly Revenue is using an online receipt tracker, where receipts have to be uploaded.

Since 2021, it has been mandatory to upload a receipt image for health and remote working expenses and it’s possible this will extend to other documentation over the new few years.

The process of uploading to the online tracker can be laborious, but one advantage is that you don’t need to retain these documents, as long as the image uploaded is readable and complete.

7. Have you set aside enough money during the year for your tax liability?

It is advisable to set aside money regularly during the year to prevent cash flow issues at the filing deadline.

Rory recommends that 30% of your profits is set aside each month, rather than trying to find a large sum all at once when filing your tax return.

You also have the option of making regular preliminary tax payments throughout the year, which is then offset against your final tax liability.

However, simply putting the money you set aside in a high-interest account is a great idea, and can potentially raise a little extra income until you need to withdraw it. Furthermore, it’s entirely possible to use the money as effectively an interest-free loan for your own business – although you’ll obviously need to ensure you can pay it back in time in order to pay your tax liability!

How do you make a payment?

You can pay by credit or debit card, but if your bank has daily transaction limits, that may not be possible.

Instead, you can pay through a ROS Debit Instruction (RDI) and this can be done after set-up. RDI is listed as an available option on the payment screen.

Final thoughts: Be organised

Do not leave it to the last minute to get your paperwork together for your tax return, as this can lead to mistakes and could potentially expose you to the possibility of a tax audit.

It’s an added stress that no business needs.

“Self-assessment doesn’t have to be overwhelming. With good planning, solid record-keeping, and awareness of current rules, you can avoid costly mistakes and make the most of available reliefs,” concludes Rory.