Each page owns one search cluster — SA100, SA800, deadline, SA302 or MTD — so answers stay focused.
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Self Assessment guides
Plain-English answers on the SA100, partnership SA800, the 31 January deadline, SA302 calculations and Making Tax Digital for Income Tax.
In short
These guides explain HMRC’s rules in plain English and how Self Assessment Software handles the same job. Start with what an SA100 is, the partnership SA800, then deadlines, SA302 reports, or MTD vs year-end filing.
How to use this handbook
We explain the rule, then how prepare-free filing works in Self Assessment Software.
Pricing, credits and “what we are not” live on the product FAQ — 50+ short answers.
What is an SA100?
The SA100 is HMRC’s main Self Assessment tax return for individuals. You use it after the tax year (6 April to 5 April) to tell HMRC about income that does not all sit in PAYE.
What is an SA800?The SA800 is HMRC’s Partnership Tax Return. It reports the partnership’s income and how profits are shared — separate from each partner’s personal SA100.
Self Assessment deadline 31 JanuaryIf you file online, HMRC must have your SA100 by 31 January after the tax year ends. Paper is due by 31 October. Partnerships also file an SA800 on the same dates for ordinary partnerships of individuals.
What is an SA302?An SA302 is HMRC’s tax calculation for a Self Assessment year. Mortgage lenders often ask for it as proof of income.
MTD for Income Tax explainedMTD for Income Tax adds quarterly updates for many self-employed people and landlords. The annual SA100 still closes the year.
FAQs
Guides hub — quick answers
Where should I start?
Start with What is an SA100? if you are new to Self Assessment. Use What is an SA800? for the partnership return, the deadline guide for 31 January, SA302 for mortgage calculations, and MTD for quarterly vs year-end.
Are these official HMRC pages?
No. They are plain-English guides from Self Assessment Software. Always confirm dates and thresholds on GOV.UK for your tax year.
Where is product pricing explained?
On Pricing and the product FAQ. Guides focus on HMRC concepts and how the desk handles them — not every commercial question.
Prepare free
Ready to file Self Assessment?
Start free, complete the SA100 when figures are ready, and pay only when you file.