The SA302 Tax Calculation: A Professional’s Guide to 2026/27

The SA302 tax calculation serves as HMRC’s official summary of a taxpayer’s income and tax liability based on their self-assessment return. The Upper Tribunal clearly defined the format and purpose of this document in Michael Kelly v The Commissioners for HMRC.

An SA302 typically features a two-sided format to ensure full transparency during tax disputes or compliance checks. The left side copies the exact figures the taxpayer declared on their return, while the right side displays any amendments HMRC has made and calculates the resulting difference in tax payable or refundable.

The way in which an SA302 is set out is the left side is copied from your decaled tax return and the right side is showing what amendments we have made and the difference in tax.

Lenders and financial institutions frequently rely on the SA302 tax calculation to verify self-employed income for mortgage applications, making its accuracy paramount for individual clients.

Core Allowances and Rates for 2026/27

When reviewing the SA302 tax calculation for the 2026/27 tax year, practitioners must account for the continued freeze on core allowances. Section 10 of the Finance Act 2026 confirms that the Personal Allowance remains frozen at £12,570, and the Basic Rate Limit remains frozen at £37,700 until the 2030-31 tax year.

Furthermore, Section 2 of the Finance Act 2026 sets the main rates of income tax for the 2026/27 tax year.

Table: Key Income Tax Parameters (2026/27)

MTD ITSA: Transforming the SA302 Tax Calculation

The 2026/27 tax year introduces a monumental shift in how HMRC captures income data. From 6 April 2026, Making Tax Digital for Income Tax Self Assessment (MTD ITSA) mandates that sole traders and landlords with a qualifying income over £50,000 must use compatible software to keep digital records and submit quarterly updates.

Under this new regime, software will provide the taxpayer with an estimated tax bill after every quarterly update.  However, these interim updates do not replace the formal SA302 tax calculation. The final tax position still only crystallises via the annual return (or end of period statement), which taxpayers must submit by 31 January following the end of the tax year.  Therefore, the definitive “SA302 style” calculation for 2026/27 will be generated upon finalisation of the digital end-of-year process.

Reconciling Capital Gains and Overpayments

The SA302 output plays a critical role in reconciling complex multi-tax liabilities, particularly concerning Capital Gains Tax (CGT) on UK property. When a taxpayer submits a 60-day CGT on UK Property Account, they may end up with an ‘initial overpayment’ of CGT once their final annual income is assessed.

HMRC uses the SA302 tax calculation output to display the final, consolidated figures for Income Tax, CGT, and Class 2 National Insurance Contributions.  For the 2021/22 tax year onwards, HMRC systems automatically offset this ‘initial overpayment’ of CGT against other Self Assessment charges to prevent the taxpayer from overpaying.

If the SA302 tax calculation shows a remaining overpaid amount after this automatic offset, HMRC will display the figure on the SA302 output, but they will not automatically repay it.  Taxpayers or their agents must contact HMRC directly to allocate the funds to other tax charges or request a manual repayment.

Late Filing and Self-Calculation

HMRC generally calculates the tax bill on behalf of the taxpayer if they submit a paper return by the 31 October deadline. If a taxpayer files a paper return after 31 October, HMRC may not process it in time to issue an SA302 before the 31 January payment deadline.

In December, HMRC issues forms SA309A or SA309C as personalised reminders to those whose returns remain unprocessed.  To avoid late payment interest and penalties, HMRC advises these taxpayers to “self-calculate” their liability rather than waiting for the official SA302 tax calculation.  Taxpayers can utilise HMRC’s online SA Tax Calculator to estimate their liability, though HMRC issues a disclaimer regarding the accuracy of these self-calculated figures.  Alternatively, taxpayers can easily view and update their tax information at any time via their digital Personal Tax Account.

Consider reviewing the specific software compatibility requirements for generating final year-end calculations under the MTD ITSA framework to ensure seamless transitions for clients exceeding the £50,000 threshold.