HMRC’s free online portal handles the vast majority of self-assessment returns perfectly well. Third-party software earns its cost by catching errors before submission, providing a clearer interface, handling complex income types more easily, and — from April 2026 — enabling MTD ITSA quarterly submissions.
Do You Need Third-Party Software?
| Situation | HMRC free service | Third-party software |
|---|---|---|
| Simple employment income + small savings | ✓ Fine | Optional |
| Self-employment income | ✓ Works | ✓ Better experience, tax estimates |
| Rental income (single property) | ✓ Works | ✓ Better for expense tracking |
| Multiple rental properties | Possible | ✓ Recommended |
| MTD ITSA required (from April 2026) | ✗ Not MTD compatible | ✓ Required |
| Complex foreign income | Possible | ✓ Recommended |
| Capital gains (shares/property) | ✓ Works | ✓ Better CGT calculation |
Software Comparison — UK Self-Assessment 2026
| Software | Annual cost | MTD ITSA | Best for |
|---|---|---|---|
| HMRC online service | Free | No | Simple returns |
| GoSimpleTax | £50 (£68 with rental) | Yes | Value; individuals; landlords |
| TaxCalc Individual | £59 | Yes | Depth; complex returns; serious self-employed |
| Taxfiler | £25 | Yes | Budget; freelancers |
| Untied | £100 | Yes | Self-employed with income tracking built in |
| QuickBooks Self-Employed | £96/yr (£8/mo) | Yes | Already using QuickBooks for bookkeeping |
| FreeAgent | £0 (via NatWest) | Yes | Freelancers/contractors using FreeAgent already |
GoSimpleTax — Best Value for Individuals
Cost: £50/year (£68 with rental income module)
GoSimpleTax is the most popular standalone self-assessment tool for individuals. Key features:
- Tax calculation updates as you enter data — you always know what you owe
- Error and warning flags before submission
- Supports employment, self-employment, rental, dividends, savings, foreign income
- Direct HMRC submission
- MTD ITSA compatible
Best for: Self-employed individuals, landlords, people with multiple income sources who find HMRC’s portal clunky.
TaxCalc — Best for Complex Returns
Cost: £59/year (Individual edition)
TaxCalc is the tool of choice for many accountants and their clients. It offers:
- The most comprehensive income type coverage of any individual product
- Capital gains tax calculator including property gains
- Partnership and trust returns
- Professional-quality error checking
- Also offers business editions for partnerships and limited companies
Best for: Complex tax situations, higher-rate taxpayers with multiple income streams, those who want accountant-grade software.
Taxfiler — Budget Option
Cost: From £25/year
Taxfiler is a cloud-based option aimed at individuals and small practices. It is straightforward, MTD ITSA compatible, and cheaper than GoSimpleTax or TaxCalc. The interface is functional rather than polished.
Best for: Straightforward self-employment or rental income on a budget.
Untied — Best for Mobile-First Self-Employed
Cost: £100/year (premium tier)
Untied is a mobile app designed specifically for self-employed people — it connects to bank feeds to categorise income and expenses automatically and generates quarterly MTD ITSA submissions. It is more expensive but integrates income tracking and tax filing in one place.
Best for: Self-employed individuals who want everything in one app and are comfortable with mobile-first tools.
MTD ITSA — What Changes From April 2026
If you are self-employed or a landlord earning above £50,000 (£30,000 from April 2027), you are legally required to:
- Submit quarterly summaries of income and expenses to HMRC (not wait until January 31)
- Submit an End of Period Statement (EOPS) and Final Declaration annually
- Use HMRC-approved MTD-compatible software to do all of this
HMRC’s free service does not support MTD ITSA. You will need one of the approved third-party tools listed above.
Quarterly submission deadlines under MTD ITSA:
| Quarter | Deadline |
|---|---|
| April 6 – July 5 | August 5 |
| July 6 – October 5 | November 5 |
| October 6 – January 5 | February 5 |
| January 6 – April 5 | May 5 |
Worked Example — Cost vs Benefit
Emma is a freelance designer earning £55,000. She currently uses HMRC’s portal but is being brought into MTD ITSA from April 2026.
| Option | Annual cost | MTD compliant | Time saving |
|---|---|---|---|
| HMRC free service | £0 | ✗ No | N/A — must change |
| GoSimpleTax | £50 | ✓ | Quarterly submissions automated |
| Untied (mobile-first) | £100 | ✓ | Income/expense tracking + tax filing |
| Accountant | £400–£800 | ✓ | Fully managed |
For Emma, GoSimpleTax at £50/year is the minimum viable option to stay MTD-compliant. For less admin, Untied’s mobile approach at £100/year suits someone who prefers to track expenses on the go.
For more on self-assessment see self-assessment guide, self-assessment deadlines, and Making Tax Digital explained.