The Self Assessment process really goes against our cultural grain. Here, in the UK, we don’t like to talk about how much money we have (or don’t have), we don’t like to talk about our personal life with strangers, and we don’t like paying large amounts of tax. And yet, here we are. 31st January 2026 is the deadline for us to do all three. We don’t have to love the process, but there are some things we can do to make it a little less painful. Here are 3 mistakes to avoid and practical tips to sail through Self Assessment season.
Mistake 1: Leaving Self Assessment to the last minute.
Please. For the love of Yorkshire tea and biscuits, do NOT wait until Friday, 30th January, to start your filing process! It will be a crazy rush; something will be forgotten, and there will be a penalty in the post.
What you should do instead: Take control
Remember, 31st January is the last day to file, not the only day to file. If you haven’t done so already just start the process right now. Take your time and submit your Self Assessment information with the peace that only the well organised and fine-free can enjoy.
Mistake 2: Missing income and expenses
Whether it’s been forgotten or “forgotten”, the result is still ruthless and expensive. Things that most people don’t realise need to be included or truly forget to report include things like bank interest, property income, side hustles (looking at you, Vinted & Ebay), and capital gains. The opposite is also true; many folks don’t claim all their allowable business expenses and miss out on welcome tax breaks.
What you should do instead: Play the long game
- Month-by-month go through bank and credit card statements and keep track of anything business-related: software, mileage, phone, small equipment, professional fees, training, etc.
- Check you’ve included all taxable income, not just from your main job. Things to consider: savings interest, dividends, rental income, and any side hustles (including places like Vinted, Ebay, Facebook Marketplace)
- Benefit from the reliable advice of a tax professional. *Ahem*, someone like us.
Mistake 3: Not preparing for “Payments on Account”
This is a real doozy. Most upstanding taxpayers don’t understand how Payment on Account works and fail to prepare for the eye-wateringly large bill which falls onto the doormat after filing their Self Assessment.
What you should do instead: Take the Self Assessment red pill
- Understand how it works. It’s mind-bending but worth it. The official HMRC guide is here, but we’ve written an equally helpful and perhaps even easier-to-understand summary here.
- Set aside a dedicated account where you can put aside a percentage of your income every month. Don’t think of it as yours; think of it as tax to be paid while earning you a little interest.
- Get us involved. Did we mention we’re really good at tax management and accounting advice?
Tame The Self Assessment Monsters For Good
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