What Does a Self Assessment Form Look Like? 2026/27 Guide

When taxpayers ask, “What does a Self Assessment form look like?”, the answer for the 2026/27 tax year depends entirely on their income level and the changing legal landscape. The traditional paper or online form is modular, meaning you only complete the sections relevant to your specific income. However, with the upcoming Making Tax Digital (MTD) mandate, the “form” is fundamentally changing from a static document to an interactive digital software dashboard.

Here is exactly what the Self Assessment tax return looks like, how it functions under the law, and how the 2026/27 rules transform it.

The Statutory Obligation: Why HMRC Issues the Form

Section 8(1) of the Taxes Management Act 1970 (TMA 1970) legally empowers HMRC to issue a notice requiring an individual to make and deliver a return containing the necessary information to establish the amounts in which they are chargeable to income tax and capital gains tax.

Furthermore, section 9(1) of the TMA 1970 dictates that this return must include a “self-assessment”.  This means the taxpayer must actively calculate the amount of tax payable based on the information contained within the return, taking into account any reliefs or allowances claimed.

HMRC holds the authority to dictate the physical and digital appearance of this form. Section 113(1) of the TMA 1970 states that any returns under the Taxes Acts shall be in such form as the Board prescribes.

The Traditional Look: The Core SA100 Form

For taxpayers not yet mandated into the MTD regime, the primary individual tax return is the SA100. Taxpayers can file this as an official paper form, or as a computer-generated electronic version that looks identical to the official HMRC form.

The core SA100 form acts as the foundation of your tax declaration. It captures your basic personal details, National Insurance number, and standard income types such as:

• Bank and building society interest.
• Dividends from shares.
• UK pensions and state benefits.
• Charitable giving (Gift Aid) and basic tax reliefs.

The Modular Structure: Supplementary Pages

Because no two taxpayers have identical financial affairs, HMRC designed the Self Assessment form as a modular system. You must include all supplementary pages indicated on the main SA100 as being necessary for your specific circumstances.

You do not submit a massive, blank document. Instead, you attach specific schedules based on your income sources.

If a taxpayer submits a return manually, HMRC processing manuals explicitly state that a custom spreadsheet, table, or list providing details (such as self-employment or partnership income) is not an acceptable substitute for the official separate supplementary pages.

The 2026/27 Revolution: The Digital Look (MTD for ITSA)

For the 2026/27 tax year, the physical and conceptual look of the tax return undergoes a massive transformation due to Making Tax Digital for Income Tax Self Assessment (MTD for ITSA).

From 6 April 2026, the law mandates sole traders and landlords to operate MTD if their total qualifying income from trading and property exceeds £50,000 for the tax year.

If a taxpayer breaches this £50,000 threshold, they will no longer see a traditional SA100 form. Instead, the “tax return” looks like a continuous digital feed managed through MTD-compatible software. The taxpayer must:

1. Keep digital records: Taxpayers must record income and expenditure electronically within the software.
2. Provide quarterly updates: The software aggregates the digital records into category totals and sends digital quarterly updates to HMRC.
3. Submit a Final Declaration: Instead of filling out a single annual SA100 form by 31 January, the taxpayer provides their final ITSA return information directly to HMRC through the MTD-compatible software API.

This fundamentally shifts the experience. Rather than filling out boxes on a static form, the taxpayer interacts with a live dashboard that categorises transactions and generates a predicted tax bill throughout the year.

For completeness, taxpayers with qualifying gross income below the £50,000 threshold for the 2026/27 tax year will continue to use the standard modular SA100 online portal or paper form until the MTD threshold drops to £30,000 on 6 April 2027.

Next steps for research: Review HMRC’s updated register of recognised MTD-compatible software providers to demonstrate the exact dashboard interfaces clients will use for the 2026/27 transition, and verify the specific API requirements for final declarations under the new digital mandate.