Q2 After Q1: 5 Mistakes to Avoid in Your Next Quarterly Update

You Filed Q1 - Now Don't Repeat the Same Mistakes in Q2

The 7 August 2026 deadline has passed and your first quarterly update is done. That's no small thing - navigating a brand-new reporting system while running a business or managing a property takes real effort. But Q2 has already started, and the window between now and the 7 November 2026 deadline is shorter than it feels. The good news is that you now have something you didn't have before: a clear picture of where things went wrong in Q1. This post works through the five most common Q1 stumbles - expense categorisation errors, missing records, reconciliation gaps, forgotten allowances, and income tracking slips - and shows you exactly how to catch each one early in Q2 before it compounds into a bigger problem.

Why Q2 Is the Quarter That Sets the Pattern

Q1 was, for most people, a baptism by fire. You were figuring out the system at the same time as trying to file accurately. Mistakes were almost inevitable. Q2 is different. You know how the process works now. You know what information you need to pull together, and - crucially - you know where your records fell short. That puts you in a much stronger position, but only if you actually act on what Q1 taught you.

Errors that compound across quarters are harder to unpick at the final declaration stage. A miscategorised expense in Q1 can skew how you categorise the same type of expense across Q2, Q3, and Q4 if you don't notice it now. Getting Q2 right is worth the effort precisely because it makes the rest of the tax year cleaner.

Mistake 1: Expense Categorisation Errors

What went wrong in Q1

The most common Q1 problem for both sole traders and landlords is putting expenses into the wrong category. MTD does not just ask for a total expenses figure - it asks you to split costs across specific headings. Goods and materials. Travel. Professional fees. Repairs and maintenance. Each one sits in a different box, and HMRC uses those splits when it risk-assesses your update.

Common culprits include: lumping professional subscriptions into office costs, claiming personal phone bills in full rather than just the business proportion, and putting landlord repair costs into a capital improvements category (which is not allowable). For a detailed look at the categories and where things typically go wrong, read our post on common MTD expense miscategories.

How to fix it in Q2

• Go back to your Q1 submission and note any categories you were unsure about at the time. Apply the correct categorisation from the start of Q2.
• If you put something in the wrong place in Q1, you can correct it - read about how to amend your MTD quarterly update after submission to understand your options.
• When a new expense comes in during Q2, categorise it immediately rather than leaving it in a holding pile. Batch categorisation at the end of a quarter is where errors multiply.
• For mixed-use costs - for example, a phone you use for both business and personal calls - only the business proportion is allowable. Our post on mixed-use expenses and MTD explains how to calculate that split properly.

Mistake 2: Missing Records

What went wrong in Q1

Plenty of people filed their Q1 update based on what they could find rather than what was actually there. Receipts had gone missing. Bank statements covered only part of the period. Cash expenses had no paper trail at all. The result was either under-claimed expenses or a figure that could not be fully evidenced if HMRC ever asked about it.

HMRC does not require you to attach receipts to your quarterly update - but it does require you to keep them. If a compliance check arrives later, you will need to produce the underlying evidence. See our post on what backup records to keep for your MTD quarterly update for a clear breakdown of what that means in practice.

How to fix it in Q2

• Set up a simple system for capturing receipts as they happen. A dedicated folder on your phone for photos of paper receipts is enough. The important thing is consistency.
• Download or request bank statements covering the Q2 period (6 July to 5 October 2026) now, rather than waiting until late October. Some banks restrict how far back you can retrieve statements online.
• If you pay for things in cash, keep a brief written log - date, amount, what it was for, and why it was a business expense. A simple spreadsheet works fine.
• Our post on how to set up a record-keeping system for MTD quarterly updates has a practical structure you can adopt from week one of Q2.

Mistake 3: Reconciliation Gaps

What went wrong in Q1

Reconciliation simply means checking that what you have recorded matches what actually happened in your bank account. Reconciliation gaps appear when you have recorded an income or expense that does not appear in your bank statement, or when a bank transaction has no corresponding entry in your records. These gaps cause problems because you cannot be confident your Q1 figures are accurate - and if they are not accurate, any comparison HMRC makes against your bank data (which it may request) will flag discrepancies.

How to fix it in Q2

• Do a monthly reconciliation rather than a quarterly one. At the end of July, August, and September, spend 20 minutes checking your recorded income and expenses against your bank statement line by line. Catching a gap one month in is far easier than unravelling three months of transactions in October.
• If you have a separate business bank account, this process is straightforward. If you use a personal account for business transactions, highlight or tag the business-related lines as you go so they do not get lost among personal spending.
• For landlords, rental income reconciliation has some specific complications - particularly around deposits and allowances. Our guide on Q2 rental income reconciliation covers those in detail.
• For a step-by-step approach to matching records to your bank account across Q2, see Q2 bank reconciliation for MTD.

Mistake 4: Forgotten Allowances

What went wrong in Q1

Allowances are reductions that lower the amount of profit you pay tax on. Many people who file without an accountant either forget allowances entirely or apply them incorrectly because they are not familiar with what is available.

The most commonly missed ones include:

• Mileage allowance: If you use your own car for business journeys, you can claim a flat rate per mile (45p for the first 10,000 miles in a tax year, 25p after that) rather than trying to claim actual running costs. You cannot claim both. Many sole traders simply forget to log business miles at all. Our post on mileage allowances for MTD explains the rules.
• Trading allowance: If your gross income from self-employment is £1,000 or under, you may be able to claim the trading allowance instead of itemising expenses. This is only relevant in specific circumstances - see trading allowance for sole traders in MTD for the detail.
• Landlord allowable expenses: Some landlords do not claim the full range of costs they are entitled to. Agent fees, insurance, and certain service charges are all potentially allowable. Read what counts as a landlord expense in your MTD quarterly update and service charges and ground rent for landlords for a more complete picture.

How to fix it in Q2

• Start a mileage log today. Note the date, start and end point, business purpose, and miles covered every time you make a business journey. A phone note or simple spreadsheet is fine.
• Review the full list of allowable expenses now, before Q2 spending has built up. Our post on self-employed business expenses in MTD is a good starting point.
• If you missed an allowance in Q1 that you are entitled to, consider whether an amendment is appropriate. Read amending your MTD quarterly update after the deadline to understand what is and is not possible.

Mistake 5: Income Tracking Slips

What went wrong in Q1

Income tracking errors are less common than expense errors, but they matter more. Under-reporting income - even accidentally - is something HMRC takes seriously. Over-reporting income means you might pay more tax than necessary at the final declaration stage.

Common income tracking slips include: forgetting cash payments received, not recording income from late-paying clients that arrived in a different month, confusing gross income (the full amount before any deductions) with net income (what arrives in your bank after fees), and landlords mixing up rental income with deposits held.

How to fix it in Q2

• Record income on the date it is received, not the date an invoice was raised. MTD for income tax uses a cash basis by default for most sole traders and landlords, which means you report money when it comes in, not when it is owed.
• If a client pays you in cash, note it immediately. Do not rely on memory at the end of the quarter.
• Landlords: rental deposits are not income - do not include them in your quarterly update figures. Only include rent actually received during the Q2 period.
• If you have multiple income sources, keep them separated in your records from the start. Our post on mixed income MTD for self-employment and property explains how to handle the split correctly.
• Our guide on sole trader Q1 MTD income mistakes has more detail on the specific ways income figures go wrong and how to prevent them in future quarters.

Building Better Habits Now (Rather Than Fixing Them in October)

The single biggest difference between a stressful Q2 and a manageable one is timing. Every one of the five mistakes above is much easier to address when you catch it in July or August than when you are reconstructing three months of transactions in late October with a week to go before the deadline.

A few habits that make a real difference:

• Set a recurring reminder to review and categorise expenses weekly. Even 15 minutes is enough to stay on top of it.
• Do a brief bank reconciliation at the end of each month.
• Keep a mileage log open on your phone and update it the same day as each journey.
• Store receipts digitally as you receive them - do not let a pile of paper accumulate.
• If you run both self-employment and property income, keep separate records for each from day one. Do not try to untangle them at quarter end.

For a more detailed approach to organising your Q2 records, see our post on how to organise your records for Q2 after your Q1 update.

A Quick Word on Amendments

If you spotted a genuine error in your Q1 submission while working through this post, do not ignore it. MTD allows you to correct a submitted quarterly update, and in many cases it is the right thing to do. What you should not do is leave a known error uncorrected and hope it balances out later - that approach tends to create problems at the final declaration stage. Read what mistakes actually matter after filing your Q1 update and which filing errors to fix now and which to leave to help you decide what action to take.

Q2 Is a Fresh Start - Make It Count

Every quarter is a chance to improve on the one before. Q1 was your first attempt at a system that is genuinely new for most sole traders and landlords in the UK. The mistakes covered here - miscategorised expenses, missing records, unreconciled figures, overlooked allowances, and income slips - are all fixable and all avoidable if you put the right habits in place now. The 7 November 2026 deadline gives you enough time to do Q2 properly. Use it.