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Making Tax Digital for Income Tax has changed how landlords report their finances to HMRC. But one question keeps coming up: has the way rental tax is actually calculated changed too? The short answer is no. The underlying maths is the same as it always was. What has changed is when you do it and how you submit the figures.
This article walks through the full calculation process step by step. It covers how to calculate your quarterly rental profit, how those figures build into an annual picture at the Final Declaration stage, and how your rental income stacks with your other earnings to produce an actual tax bill. If you have been unsure about the mechanics behind MTD, this guide explains it in plain terms.
KEY TAKEAWAYS
The core rental tax formula has not changed under MTD: rental income minus allowable expenses equals net rental profit
Quarterly updates are summaries that inform HMRC of your income and expenses. They do not produce a tax bill
Your confirmed tax liability is calculated at the Final Declaration stage, after all four quarterly updates have been submitted
Rental profit is added to all your other income sources before the tax bands are applied. It does not sit in its own separate tax calculation
Under Section 24, mortgage interest is not deducted as an expense. A 20 percent basic-rate tax credit is applied against the final tax bill instead
Payment dates have not changed. Tax is paid through the payments on account system, not at the quarterly update stage
What MTD Actually Changes About Your Tax Calculation
The biggest source of confusion around MTD for Income Tax is the relationship between quarterly updates and the tax bill itself. Understanding this distinction makes the whole system much easier to navigate.
MTD changes the rhythm and method of reporting. Instead of completing one Self Assessment return each January, landlords now submit quarterly updates throughout the year, followed by a Final Declaration at the end. But the tax calculation itself, the formula that determines how much you owe, has not changed.
Quarterly updates are summaries, not tax returns
Each quarterly update is a summary of your rental income and expenses for that three-month period. You are telling HMRC what came in and what went out. You are not submitting a tax return and you are not being assessed for tax at this stage.
HMRC uses the data from your quarterly updates to generate a running estimate of your likely tax position for the year. This estimate appears in your MTD software and is useful for planning ahead. But it is an estimate, not a final figure, and no tax is charged or collected as a result of submitting a quarterly update.
Where the actual tax calculation happens
The legal tax liability is calculated and confirmed at the Final Declaration stage. This is submitted after all four quarterly updates for the tax year have been completed. At this point, all the quarterly figures are aggregated, year-end adjustments are applied, other income sources are added in, and the software runs a full calculation to arrive at your confirmed tax bill.
Important
The Final Declaration must be submitted through your MTD-compatible software by 31 January following the end of the tax year. From April 2026 onwards, HMRC's own online filing service is closed to MTD users for this purpose. The submission must go through software.
The Rental Income Calculation: What Goes In and What Comes Out
Before your tax liability can be worked out, you need to know your net rental profit. This is the figure that flows into the wider income tax calculation.
Gross rental income
Rental income covers everything you receive from letting your properties. This includes rent collected from tenants, any service charges you receive, and ground rent income if you are a freeholder letting property.
How you record income depends on your accounting basis. Most landlords use the accruals basis, which means recording income in the period it was earned, regardless of when it was received. Some landlords elect to use the cash basis instead, which means recording income when the money actually arrives. Your MTD software should be set up to reflect whichever basis applies to you.
Security deposits are not rental income when received. You only include a retained deposit as income in the tax year when you formally determine that you are entitled to keep it.
Allowable expenses
Once you have your gross rental income, you deduct allowable expenses to arrive at your net profit. Allowable expenses are the genuine costs of running your rental property. These include letting agent fees, property repairs and routine maintenance, buildings and contents insurance, professional fees such as accountancy costs and legal advice relating to the letting, utility bills you pay directly as the landlord, council tax where you are responsible for it, and the cost of services you provide to tenants.
Mortgage interest is handled differently under Section 24, which is covered further below. What is important to know at this stage is that it is not deducted as a straightforward expense the way it was before Section 24 came in.
Capital spending does not count as an allowable expense. If you install a new bathroom, add an extension, or replace a kitchen as an improvement rather than a like-for-like repair, that cost is capital expenditure. Including it as an allowable expense would reduce your reported profit incorrectly and create a problem when the figures are reconciled at the Final Declaration stage.
The core formula
The calculation is straightforward:
The Rental Profit Formula
Rental Income received minus Allowable Expenses equals Net Rental Profit (or Loss)
Worked Example
A simple example: you receive £9,000 in rent during a quarter. Your allowable expenses for that quarter total £3,200, covering agent fees, insurance, and a boiler repair. Your net rental profit for that quarter is £5,800. That figure goes into your quarterly update. No tax is due at this point. The £5,800 is one building block in your annual picture.
How the Quarterly Updates Build Your Annual Picture
Cumulative reporting across four quarters
Each quarterly update covers one of the four tax year periods. The standard quarters run from 6 April to 5 July, 6 July to 5 October, 6 October to 5 January, and 6 January to 5 April. Landlords who prefer to align with calendar months can elect to use calendar quarters instead, but this election must be made through the software before the first quarterly update of the year is submitted.
As you submit each update, your MTD software tracks the cumulative income and expense figures and updates the running tax estimate. This means that by the time you reach the fourth quarter, you already have a good picture of where your tax position is likely to land.
Worked Example
Here is how the figures build across a tax year for a landlord with two residential properties.
Quarters | Rental income | Allowable expenses | Quarterly profit |
|---|---|---|---|
Quarter 1 | £9,000 | £3,200 | £5,800 |
Quarter 2 | £9,000 | £2,400 | £6,600 |
Quarter 3 | £9,500 | £4,100 | £5,400 |
Quarter 4 | £8,500 | £2,800 | £5,700 |
Annual Figure | £36,000 | £12,500 | £23,500 |
Year-end adjustments at the Final Declaration stage
Before the Final Declaration is submitted, the software applies any year-end adjustments that were not captured in the quarterly updates. This is where capital allowances are applied on qualifying items such as office equipment or tools used in managing the property. Any losses carried forward from previous years are applied here too. If any non-allowable costs slipped through during the quarterly updates, such as capital spending entered incorrectly as a repair, those are added back at this stage.
Adjustment Example
After adjustments, the figure becomes your final taxable rental profit for the year. In the example above, if capital allowances of £600 apply, the final taxable rental profit comes to £22,900.
How Rental Profit Becomes a Tax Bill
Rental profit combines with all your other income
Rental profit is not taxed in isolation. It is added to your other sources of income for the year, which may include employment income from a job, pension income, savings interest, and any self-employment profit. The combined total is your total income, and your income tax liability is calculated on that combined figure after the personal allowance is deducted.
This matters because rental profit can push you into a higher tax band. If your employment income already takes you close to the basic rate threshold, rental profit on top of that may mean part of your income is taxed at 40 percent rather than 20 percent.
Current Income Tax Bands · England, Wales and Northern Ireland
Personal Allowance: £12,570 (tax-free)
Basic rate: 20% on income from £12,571 to £50,270
Higher rate: 40% on income from £50,271 to £125,140
Additional rate: 45% on income above £125,140
Adjustment Example
Landlord with employment income
Take a landlord who earns £32,000 from employment and has a taxable rental profit of £22,900 after adjustments.
Step one: total income is £32,000 plus £22,900, which equals £54,900
Step two: deduct the personal allowance of £12,570 to give taxable income of £42,330
Step three: the first £37,700 of taxable income falls within the basic rate band and is taxed at 20%, giving £7,540. The remaining £4,630 falls into the higher rate band and is taxed at 40%, giving £1,852
Total income tax before any credits: £9,392
Mortgage interest and Section 24: how it affects the calculation
Since Section 24 was fully phased in, landlords can no longer deduct mortgage interest directly from rental income as an expense. Instead, basic-rate tax relief of 20 percent is applied as a tax credit against the final income tax bill.
In practice this means your rental profit figure is higher than it would have been under the old rules, which can push more of your income into the higher rate band. The 20 percent credit is then applied after the tax has been calculated.
SECTION 24 Credit Example
Using the example above, if your annual mortgage interest is £6,000, the Section 24 credit is £1,200.
This is deducted from the tax figure of £9,392 to give a final income tax liability of £8,192.
Understanding this is essential because it means higher-rate taxpayers often pay more in tax on rental income than a headline look at their expenses would suggest.
Payment: When the Tax Bill Is Actually Due
MTD does not change the dates on which tax is paid. You continue to pay through the Self Assessment payments on account system. The first payment on account is due by 31 January during the tax year. The second is due by 31 July. Any balancing payment, which is the difference between what you paid on account and what you actually owe, is due by 31 January following the end of the tax year. This is the same deadline as the Final Declaration itself.
Quarterly updates do not trigger any payment obligation. No tax is collected at the quarterly stage, regardless of how much profit the update reports.
What Can Go Wrong: Common Calculation Errors Under MTD
Treating capital spending as a repair
This is the most common mistake. Replacing an entire kitchen, adding a new bathroom, or carrying out structural work is capital expenditure, not a repair. Entering it as an allowable expense reduces your quarterly profit figure incorrectly. At the Final Declaration stage, those costs need to be removed, which can produce an unexpected upward revision to your taxable profit and your tax bill.
Forgetting to add other income before the Final Declaration
Your MTD software calculates a running tax estimate based only on the income sources it knows about, which are your rental and self-employment income. Before you can submit the Final Declaration, you must report all other taxable income too. This includes employment income, savings interest, dividends, and pension income. If you do not include these, the tax figure shown by the software is incomplete, and the confirmed tax bill will be wrong.
Misunderstanding the mortgage interest position
Some landlords still enter mortgage interest as a full deductible expense in their quarterly updates. Under Section 24, it should be recorded separately and applied as a 20 percent credit at the Final Declaration stage, not deducted as an expense against rental income. Entering it incorrectly will produce an understated profit figure in the quarterly updates and a correction will be needed when the Final Declaration is prepared.
Conclusion
Mastering the MTD tax calculation as a landlord is less about learning new maths and more about understanding where in the process the numbers land. The quarterly updates build your picture throughout the year. The Final Declaration is where everything comes together and your actual tax liability is confirmed. Once that rhythm is clear, the system is far more manageable than it first appears.
Frequently Asked Questions
