The £1,000 Tax Saver Checklist
Who this is for
This checklist is for anyone filing a UK Self Assessment tax return. That means employees, sole traders, landlords, and people with a job plus side income.
How to use it:
Tick each box you are already doing
Every box you can't tick is either money you may be missing or a fine you could avoid
Each section shows a worked example, so you can see what a missed item is really worth
The examples use 2025/26 rates. Your own saving depends on your income and tax band, so treat them as examples, not promises.
1. Deadlines and fines
The online return for 2025/26 is due by 31 January 2027. Miss it by one day and HMRC charges £100, even if you owe no tax.
Key dates:
5 October 2026: deadline to register if you are new to Self Assessment
31 October 2026: deadline for paper returns
31 January 2027: online return due. Pay the 2025/26 balance plus your first payment on account for 2026/27
31 July 2027: second payment on account for 2026/27
Late filing fines (they stack up):
1 day late: £100
3 months late: £10 a day, up to £900
6 months late: £300 or 5% of the tax owed, whichever is more
12 months late: another £300 or 5%, whichever is more
Worked example: file six months late with nothing owed and the fines alone come to £1,300 (£100 + £900 + £300). Late payment adds interest and its own extra charges.
☐ I know my filing deadline and have it in my calendar
☐ I have my HMRC login (Government Gateway) and my UTR number ready
☐ I plan to file by December, not the last week of January
☐ If I can't pay in full, I know I can ask HMRC for a payment plan before the deadline
2. Free allowances most people forget
These are amounts you can earn or claim with little or no tax. Many people never check them.
Personal Allowance (£12,570): income you pay no Income Tax on
Trading Allowance (£1,000): the first £1,000 of side-business income can be tax-free
Property Allowance (£1,000): the first £1,000 of rental income can be tax-free
Marriage Allowance (£1,260 transferred): saves a couple up to £252 a year
Personal Savings Allowance (£1,000 basic rate, £500 higher rate): bank interest you pay no tax on
Dividend Allowance (£500): dividends you pay no tax on
Catch: you use the Trading or Property Allowance instead of claiming your real expenses, not as well as. Pick whichever gives the bigger number.
Worked example: Sam earns £900 a year selling crafts with £100 of costs. Using the Trading Allowance, Sam pays no tax on it and may not need to report it at all.
☐ I've checked if the Trading or Property Allowance beats claiming my actual costs
☐ If one of us earns under £12,570, we've claimed Marriage Allowance (you can backdate it up to 4 years)
☐ I've included all bank interest and know if I'm over my savings allowance
3. Sole traders: costs you can claim
Every £1 of allowed cost cuts your profit by £1. For a basic-rate sole trader, that saves about 26p (20% Income Tax plus 6% Class 4 National Insurance).
Worked example: you drive 5,000 business miles in your own car. At HMRC's 45p a mile, that's £2,250 off your profit, or about £585 less tax for a basic-rate taxpayer.
Running costs:
☐ Business mileage at 45p a mile for the first 10,000 miles, then 25p (or a share of real car costs, not both)
☐ Working from home: HMRC flat rate of £10, £18 or £26 a month for 25 to 50, 51 to 100, or 101+ hours, or a fair share of real bills
☐ The business share of my phone and internet
☐ Software, apps and subscriptions used for the business
☐ Insurance, bank charges and accountant's fees
☐ Advertising, website costs and trade body memberships
☐ Training that keeps my current skills up to date
☐ Food and drink only when travelling away from my usual place of work
Bigger items:
☐ Laptops, tools and equipment (most small businesses can claim the full cost in the year they buy them)
☐ I've kept receipts for anything I bought before I started trading, which can sometimes be claimed
Things HMRC usually says no to:
☐ I'm not claiming everyday clothes (only uniforms or safety gear)
☐ I'm not claiming client meals or entertaining
☐ I'm not claiming travel to the same regular workplace every day
Made a loss? You may be able to set it against other income, like a salary, and get tax back. Ask before you file.
4. Landlords
The biggest landlord mistake is getting mortgage interest wrong. For homes you let, you can't take it off your rent. Instead you get a tax cut worth 20% of the interest.
Worked example: you pay £6,000 a year in mortgage interest. You get £1,200 off your tax bill (20% of £6,000). If you forget to enter it, you lose that £1,200.
☐ I've entered my mortgage interest in the right box (finance costs), not as a normal expense
☐ Only the interest is claimed, not the part of the payment that pays off the loan
☐ Letting agent fees, landlord insurance, ground rent and service charges
☐ Safety checks: gas certificate, electrical check, smoke alarms
☐ Repairs that put things back as they were (not upgrades or extensions)
☐ Replacing furniture, white goods or carpets with like-for-like items
☐ Travel to the property for landlord jobs
☐ Costs from before the first tenant moved in (some can be claimed)
☐ If I own with a partner, the income is split the right way between us
☐ If I had a furnished holiday let, I know those special rules ended in April 2025
Sold a rental property? Capital Gains Tax must be reported and paid within 60 days of completion. That is separate from your normal tax return.
5. A job plus side income
Your job already uses your tax-free allowance, so side income is usually taxed from the first pound above any allowance. That makes the checks below matter more.
☐ I've checked my tax code on my payslip is right (a wrong code means wrong tax all year)
☐ I've claimed job costs my employer didn't pay back: work uniform washing, professional body fees, business mileage in my own car
☐ I've used the Trading Allowance or real costs on my side income, whichever is better
☐ I know online platforms (like eBay, Etsy and Airbnb) now send sellers' details to HMRC
☐ My P60 and any P11D figures match what I've put on my return
☐ If I have a student loan, I've checked whether side income may increase my repayments
Worked example: a higher-rate taxpayer pays £200 a year to a professional body HMRC accepts. Claiming it saves £80 a year, and you can backdate up to 4 years.
6. Pensions, charity and the high-income traps
If you pay higher-rate tax, you only get your full pension tax relief by claiming it on your return. HMRC does not add it for you.
Worked example: you pay £4,000 into a personal pension. Your provider tops it up to £5,000. As a higher-rate taxpayer you can claim another £1,000 back, but only if you put the £5,000 on your return.
☐ I've entered personal pension payments (not ones taken through my payroll)
☐ I've entered Gift Aid donations (higher-rate taxpayers get extra relief here too)
☐ If my income is near £60,000 and we get Child Benefit, I've checked the High Income Child Benefit Charge (it applies between £60,000 and £80,000)
☐ If my income is between £100,000 and £125,140, I know I lose my tax-free allowance there, so each extra £1 is taxed at about 60%
☐ I know pension payments and Gift Aid can pull my income below both of those lines
☐ If family members genuinely help in my business, I pay them a fair rate and keep records
Worked example: your income is £110,000. A £8,000 pension payment (£10,000 once the provider adds tax relief) brings your income back to £100,000. The total tax saved is about £6,000 on that £10,000.
7. Payments on account and getting money back
If your tax bill is over £1,000, HMRC usually asks you to pay half of next year's bill in advance, twice a year. This is the big January shock for first-year filers.
Worked example: your first bill is £4,000. In January you pay £4,000 plus a £2,000 advance payment, so £6,000 is due at once. Another £2,000 is due in July.
☐ I'm saving for tax as I earn (for example, 25 to 30% of profit into a separate pot)
☐ If my income has dropped this year, I've asked HMRC to reduce my payments on account
☐ I know I can fix a mistake on my return for up to 12 months after the 31 January deadline
☐ If I paid too much tax in an earlier year, I know I can claim it back for up to 4 years
Only reduce payments on account if you're confident. Cutting them too far means interest on the shortfall.
8. Making Tax Digital and record keeping
Making Tax Digital (MTD) means sending HMRC updates every three months using approved software. It has already started for some people.
Who must join:
From April 2026: self-employment plus rental income over £50,000 a year (before costs)
From April 2027: over £30,000
From April 2028: over £20,000
The test uses your total sales and rents before costs, not your profit.
☐ I've checked whether I'm already in MTD or will be next April
☐ My records are in software or a spreadsheet I can link to software
☐ I use a separate bank account for business or rental money
☐ I keep receipts and records for at least 5 years after the 31 January deadline
☐ I watch my sales over the last 12 months against the £90,000 VAT threshold
9. Ten-minute final check before you press submit
☐ All income is included: job, self-employment, rent, interest, dividends, platform sales
☐ Figures match my P60, bank statements and rental statements
☐ I've ticked the right boxes for student loan and Child Benefit
☐ Pension and Gift Aid payments are entered
☐ I've saved a PDF copy of the return and the HMRC submission receipt
Got gaps? Let's fix them
Most people can't tick every box, and that's normal. Each gap is either money you may be owed or a fine you can avoid.
Book a free 20-minute call. We'll go through the boxes you left blank, tell you which ones matter for you, and give you a clear plan before 31 January.