7 Costly Mistakes Landlords Make On Their Self-Assessment

Completing a self-assessment tax return can feel like a chore, but for landlords, getting it right can save you time, stress, and money. Unfortunately, many landlords fall into common traps, leading to missed deductions, overpayments, or last-minute panic.

In this guide, we’ll break down the 7 costly mistakes landlords make on their self-assessment and give you practical tips to avoid them. We’ll also show you how Landlord Studio can make the process smoother, helping you stay organised and on top of your taxes.

1. Misreporting In Your Self-Assessment for Rental Income

One of the most common mistakes landlords make is misreporting rental income when completing their self-assessment for rental income. Rental income includes more than just the monthly rent payments; it also covers:

• Additional service fees (e.g., cleaning, gardening, or maintenance)
• Non-refundable deposits retained due to property damage or unpaid rent
• Reimbursements for utilities, council tax, or repairs paid on behalf of tenants

Example of Misreporting

❌ Incorrect: Only reporting monthly rent (£1,000) and excluding a £150 cleaning fee.
✅ Correct: Reporting both the monthly rent (£1,000) and the cleaning fee (£150), totaling £1,150.

Step-by-Step Guide to Avoid Misreporting

1. Log all payments received from tenants immediately.
2. Categorise income sources clearly (e.g., rent, service fees, reimbursements).
3. Use a dedicated tool like Landlord Studio to automate income tracking and prevent errors.

2. Missing Out on Claiming Allowable Expenses in Your Landlord Self-Assessment

Many landlords miss valuable deductions by not claiming all allowable expenses in their landlord self-assessment. These expenses can significantly reduce your taxable profit and include:

• Repairs and maintenance (e.g., fixing a leaky tap)
• Mortgage interest relief (claimed as a 20% tax credit)
• Landlord insurance premiums
• Property management fees
• Legal and accounting fees
• Travel expenses (e.g., mileage for property visits)
• Advertising costs for finding tenants

Example of a Missed Deduction

❌ Incorrect: Forgetting to claim £500 spent on advertising a vacant property.
✅ Correct: Claiming the £500 advertising cost to reduce your taxable profit.

Step-by-Step Guide to Claiming Expenses

1. Track expenses in real-time rather than waiting until the end of the tax year.
2. Keep digital copies of all receipts and invoices.
3. Use Landlord Studio to scan and store receipts, categorise expenses, and ensure nothing is missed.

3. Missing the Self-Assessment Deadline for Rental Income

Nobody enjoys deadlines, but missing the submission date for your self-assessment for rental income can lead to penalties. The key dates to remember are:

• 31st October for paper returns
• 31st January for online returns

Penalties for Late Submission

• £100 fine for missing the deadline.
• £10 per day if you’re more than three months late (up to 90 days).
• Interest charges on unpaid taxes.

Learn more about penalties on the HMRC website.

Quick Tips to Stay on Track

1. Set multiple reminders leading up to the deadline.
2. Submit early to give yourself time to fix errors.
3. Use Landlord Studio's reminder and calendar features to ensure you never miss a deadline.

4. Not Keeping Proper Records for Your Rental Income Self-Assessment

Good record-keeping is the backbone of a stress-free rental income self-assessment. More than this however, with Making Tax Digital being phased in for landlords from April 2026 landlords will be required to keep accurate up-to-date records using a digital, HMRC recognised, software or fall foul of the new tax regulations.

HMRC expects landlords to keep records of:

• Rental payments (dates and amounts)
• Receipts for repairs and services
• Invoices for property management fees
• Bank statements showing rental transactions

Example of Poor Record-Keeping

❌ Incorrect: Storing all receipts in a shoebox and losing track of some expenses.
✅ Correct: Using a digital system to log and categorise each expense as it happens.

Step-by-Step Guide to Good Record-Keeping

1. Use a dedicated bank account for rental transactions. These can be connected to Landlord Studio allowing you to quickly reconcile transactions as they occur.
2. Scan receipts immediately using an app like Landlord Studio.
3. Keep detailed logs of travel, maintenance, and communications with tenants.

Make Record-Keeping Easy With Tools Designed For You

Create your free account with Landlord Studio and upgrade your buy-to-let accounting today. Landlord Studio will be integrated with the HMRC and compliant with MTD regulation requirements before the 2026 deadline.

5. Not Referring to a Landlord Tax Return Example

Filing a tax return can be confusing, especially if you’re new to it. Not checking a landlord tax return example can lead to simple mistakes. An example can show you:

• How to complete each section correctly
• What expenses to include and where to list them
• How to calculate your taxable profit accurately

Quick Tips for Using a Tax Return Example

1. Visit the HMRC website for official examples and guidelines. 
2. Look for examples specific to rental income rather than general self-assessments.
3. Use Landlord Studio to guide you through the process with tailored insights.

6. Issues with Joint Ownership and Self-Assessment

Whenever a rental property is owned jointly, each owner must declare their share of rental income and expenses. A common error is incorrectly dividing income and expenses - this can lead to inconsistencies with HMRC. 

An Example of a Joint Ownership Mistake

❌ Incorrect: Reporting the full rental income ($12,000) under one owner instead of splitting it equally (£6,000 each).
✅ Correct: Each owner records their share of the income and expenses accurately.

How to Avoid This Mistake

1. Agree on the split of income and expenses prior to renting out a property (for most joint ownership setups, this split would be based on ownership percentages). 
2. Maintain separate records for each owner. 
3. Use Landlord Studio to keep accurate records for multiple owners.

7. Ignoring Capital Gains Tax When Selling a Property

Many landlords forget about Capital Gains Tax (CGT) when selling a rental property. If your property has increased in value, you’ll need to pay CGT on the profit. 

Example of a CGT Mistake

❌ Incorrect: Selling a property for £250,000 (bought for £200,000) and not accounting for the £50,000 gain.
✅ Correct: Reporting the £50,000 gain and applying available reliefs (e.g., annual exemption).

How to Avoid This Mistake

1. Calculate potential CGT prior to selling a property. 
2. Consider timing the sale to make the most of your annual CGT allowance (£3,000 for 2024/25).
3. Seek professional advice for situations you are unsure of. 

Long-Term Effects of These Self-Assessment Mistakes

Making mistakes on your self-assessment can have consequences that extend beyond immediate penalties. These can include:

• Higher Tax Bills: Missing deductions means you pay more tax than necessary.
• HMRC Audits: Repeated errors may trigger an audit, which can be stressful and time-consuming.
• Loss of Credibility: Inaccurate reporting can affect your standing with lenders if you need future financing.
• Interest and Penalties: Delays and errors can lead to compounded interest and fines over time.
• Cash Flow Issues: Unexpected tax bills can disrupt your cash flow and impact your property investments.

Self-Assessment Mistakes and Changing Regulations for Landlords

Landlords must also be aware of the upcoming regulation changes to how they will be required to record and report their rental income on their self-assessments.

Making Tax Digital, set to be phased in for landlords earning above the £50,000 threshold from April 2026. This will require landlords to keep digital records of their finances and submit quarterly updates before a final end of year submission.

This represents a major shift in how landlords will be required to operate and track their finances, and requires landlords to adopt an MTD compliant and HMRC recognised software to keep their accounts up to date throughout the year.

Learn more about Making Tax Digital for Landlords

Landlord Self-Assessments and How Landlord Studio Can Help

Filing your self-assessment doesn’t have to be stressful. Landlord Studio offers a complete set of tools designed with the sole purpose of helping landlords to manage their finances with ease. It offers: 

• Deadline Reminders: Set alerts so you never miss a deadline.
• Custom Reports: Generate financial reports to simplify tax returns.
• Joint Ownership Tools: Filter reports by owners.
• Automated Income Tracking: Log every payment effortlessly.
• Expense Management: Scan receipts, track mileage, and categorise expenses.

Get started with Landlord Studio today and make tax season a breeze!

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