Quarterly Updates vs Final Declaration: MTD ITSA Filing Explained

If you're preparing for Making Tax Digital for Income Tax (MTD ITSA), you've probably heard about "quarterly updates" and "final declarations" - but what's the difference? Quarterly updates are summaries during the year. The final declaration replaces your Self Assessment tax return at the end. Both are mandatory.

This guide explains exactly what each filing does, when you need to submit them, and how they work together in the new MTD system.

The Short Answer: Two Different Jobs

Here's the key distinction:

• Quarterly updates - Progress reports showing your income and expenses for each quarter
• Final declaration - Your actual tax return, including final calculations, deductions, and tax owed

Think of quarterly updates as giving HMRC a running commentary on your business. The final declaration is where you actually calculate and declare your tax liability for the year.

What Are Quarterly Updates?

Quarterly updates are summary reports of your business income and expenses. You submit four per tax year for each income source, covering (on standard quarters):

• Q1: 6 April to 5 July (due 7 August)
• Q2: 6 July to 5 October (due 7 November)
• Q3: 6 October to 5 January (due 7 February)
• Q4: 6 January to 5 April (due 7 May)

The Q4 update is a separate submission, due by 7 May. It is not rolled into the final declaration.

What Goes in a Quarterly Update

Each quarterly update includes:

• Total income received during the quarter
• Business expenses paid during the quarter (on the cash basis)
• Basic categorisation of income and expense types

You don't calculate tax owed in quarterly updates. They're purely informational - showing HMRC what's happened in your business during that three-month period.

What Quarterly Updates Don't Include

Quarterly updates are deliberately limited. They don't include:

• Annual allowances (like the £1,000 trading allowance)
• Capital allowances for equipment purchases
• Pension contributions
• Other income sources (employment, savings, etc.)
• Tax calculations
• Personal allowance deductions

This is why quarterly updates alone can never replace your tax return.

What Is the Final Declaration?

The final declaration is your actual tax return under MTD. It's due by 31 January following the end of the tax year (the same deadline as the old online tax return) - 31 January 2028 for 2026-27.

This is where you:

• Confirm your total income for the year
• Apply annual allowances and deductions
• Include other income sources
• Calculate your actual tax liability
• Declare how much tax you owe or are owed

How the Final Declaration Uses Quarterly Updates

Your MTD software pulls together all four quarterly updates to create the final declaration. But you can still make adjustments at this stage.

For example, if you:

• Forgot to claim an expense in Q2
• Need to apply capital allowances for equipment
• Want to claim the £1,000 trading allowance instead of actual expenses

You can make these corrections in your final declaration. The quarterly updates become the foundation, but the final declaration is where everything gets finalised.

Why Both Are Required

HMRC requires both quarterly updates and final declarations because they serve different purposes:

Quarterly Updates Give HMRC Visibility

Regular updates help HMRC:

• Track business performance in real-time
• Identify potential issues early
• Reduce the "big surprise" of annual tax bills
• Spot unusual patterns or potential errors

Final Declarations Provide Legal Certainty

The final declaration:

• Creates your legal tax liability for the year
• Applies all allowances and deductions correctly
• Includes income from all sources
• Provides the final, auditable record

Common Misconceptions

"Quarterly Updates Are Just Estimates"

Wrong. Quarterly updates must reflect your actual records for that period. If you invoiced £2,000 in June, you report £2,000 - not an estimate or average.

"I Don't Need a Final Declaration If I File Quarterly"

Partly right. Quarterly updates don't replace the annual return - but the final declaration does. Once you're in MTD, you don't file a separate Self Assessment return as well.

"I Can Skip Quarters If Business Is Quiet"

Wrong. Even if you earned nothing in a quarter, you still need to submit a quarterly update showing £0 income. Missing quarterly deadlines earns penalty points from 2027-28, regardless of your income level.

"Quarterly Updates Calculate My Tax Bill"

Wrong. Quarterly updates are pure data reporting. Tax calculations only happen in your final declaration.

Practical Example: How It Works Together

Let's follow Sarah, a freelance graphic designer, through her first MTD year:

Q1 Update (Due 7 August)

Sarah reports:

• Income: £4,500
• Expenses: £800

Q2 Update (Due 7 November)

Sarah reports:

• Income: £3,200
• Expenses: £1,200 (including new laptop)

Q3 Update (Due 7 February)

Sarah reports:

• Income: £2,800
• Expenses: £600

Q4 Update (Due 7 May)

Sarah reports:

• Income: £3,100
• Expenses: £700

Final Declaration (Due 31 January)

Sarah's software combines her four quarterly updates. Her total year shows £13,600 income and £3,300 expenses.

But in her final declaration, Sarah decides to:

• Confirm her annual adjustments (on the cash basis her laptop is already an expense, so no capital allowance is needed)
• Add her bank interest (£45)
• Apply her personal allowance (£12,570)

The final declaration calculates her actual tax owed - something the quarterly updates never did.

Record-Keeping for Both

Both quarterly updates and final declarations need the same underlying records. You need to track:

• All business income (invoices, cash sales, etc.)
• All business expenses with receipts
• Bank statements
• Mileage logs (if claiming vehicle expenses)

HMRC's record-keeping requirements apply to both types of filing. The difference is timing - quarterly updates use records from specific three-month periods, while final declarations use the complete annual picture.

Penalties for Getting It Wrong

Missing quarterly updates and final declarations both trigger separate penalties:

Late Submission Penalties

• Each missed deadline earns one penalty point (one per deadline, even with several income sources)
• At 4 points you get a £200 penalty, then £200 for each further late submission
• A late final declaration earns a point too
• Applies even if you owe no tax

Late Payment

• 3% of tax unpaid at day 15, a further 3% at day 30, then 10% a year
• Plus interest at the Bank of England base rate plus 4%

Software Requirements

You need MTD-compatible software to submit both quarterly updates and final declarations. Standard accounting software won't work - it must be specifically approved for MTD submissions.

MTD bridging software handles both types of filing from the same set of records. You enter your income and expenses once, then the software generates both quarterly updates and your final declaration when needed.

Timeline Overview

Here's how the MTD year flows:

1. 6 April: New tax year starts
2. 7 August: Q1 update due
3. 7 November: Q2 update due
4. 7 February: Q3 update due
5. 5 April: Tax year ends
6. 7 May: Q4 update due
7. 31 January (following year): Final declaration due, and any tax owed paid

Each deadline is independent. You can't "catch up" by filing everything together at year-end.

Key Takeaways

Quarterly updates and final declarations are both essential parts of MTD ITSA, but they do different jobs. Quarterly updates track your progress through the year, while your final declaration calculates and declares your actual tax liability. Missing either triggers penalties, so understanding both requirements - and having the right software to handle them - is crucial for MTD compliance.