If you earn income in the UK that isn’t fully taxed through PAYE — such as self-employment income, rental income, foreign income, or investment gains — you’ll need to complete an SA100 form as part of your Self-Assessment tax return.
The SA100 is the main UK tax return used to report your income and calculate how much tax you owe (or are due back). This guide explains what the SA100 is, who needs it, deadlines, and how to file it correctly.
What Is the SA100 Form?
The SA100 is the core Self-Assessment tax return submitted to HM Revenue & Customs (HMRC).
It is used to declare:
- income earned during the tax year
- allowable expenses and reliefs
- capital gains
- tax already paid
- final tax owed or refund due
The SA100 acts as the main return, with additional supplementary pages added depending on your situation (e.g. SA105, SA109).
Important:
The SA100 itself does not contain all income details — it works together with supplementary forms.
Who Needs to File an SA100?
You usually need to file an SA100 if you are:
- Self-employed or a sole trader
- A UK landlord
- A non-resident landlord
- An expat with UK income
- Receiving foreign income
- A company director (in some cases)
- Earning income not fully taxed through PAYE
Even if you live abroad, you may still need an SA100 if you have UK-source income.
SA100 for Non-Resident Landlords & Expats
If you are non-UK resident, the SA100 is still required to report UK income such as:
- rental income from UK property
- UK employment income
- UK pensions or investment income
In these cases, the SA100 is usually submitted together with:
- SA109 – to confirm non-residence or split year treatment
- SA105 – if you earn UK rental income
What Income Is Reported on the SA100?
The SA100 works as a summary return, supported by supplementary pages. Income reported can include:
- Employment income
- Self-employment profits
- Rental income
- Savings & interest
- Dividends
- Capital gains
- Foreign income
HMRC uses this information to calculate:
income tax National Insurance (if applicable) payments on account
How Do You Get the SA100 Form?
You can access the SA100 in two ways:
- Digitally via HMRC-recognised tax software
- Paper form (downloaded from HMRC)
Note:
Paper filing is becoming increasingly restricted, and many non-residents cannot use HMRC’s standard online portal. Approved software or an accountant is often required.
How to Complete the SA100 Correctly
At a high level, completing the SA100 involves:
- Providing personal details (name, address, UTR)
- Declaring all relevant income
- Adding supplementary pages where required
- Claiming allowable expenses & reliefs
- Reviewing the tax calculation
- Submitting the return to HMRC
Accuracy is critical — errors can result in penalties, interest, or HMRC enquiries.
SA100 Deadlines (2024/25 Tax Year)
- Register for Self-Assessment: 5 October 2025
- Paper filing deadline: 31 October 2025
- Online filing deadline: 31 January 2026
- Tax payment deadline: 31 January 2026
Missing deadlines can trigger automatic penalties, even if no tax is owed.
SA100 Late Filing Penalties
- 1 day late: £100 penalty
- 3 months late: £10 per day (up to £900)
- 6 months late: £300 or 5% of tax due
- 12 months late: further £300 or 5% of tax due
Interest also accrues on unpaid tax.
How We Help With SA100 Tax Returns
We specialise in:
- SA100 Self-Assessment tax returns
- Non-resident & expat filings
- UK landlords & overseas landlords
- SA105 & SA109 submissions
- HMRC-compliant digital filing
We ensure: correct tax treatment no overpayment full compliance fast, stress-free filing
Do You Need Help Filing an SA100?
If you:
- earn income outside PAYE
- live abroad but earn UK income
- rent out UK property
- are unsure which forms apply
We’ll handle your SA100 from start to finish.
SA100 FAQs
What is an SA100?
The SA100 is the main UK Self-Assessment tax return used to report income and calculate tax owed.
Is the SA100 the same as Self-Assessment?
Yes — the SA100 is the core Self-Assessment return.
Can non-residents file an SA100?
Yes, if they earn UK-source income.
Can I file an SA100 online?
Yes, using HMRC-recognised software or an accountant.
Do I need SA100 if I’m a landlord?
Yes — landlords must file an SA100 with an SA105.
