Jargon-free personal tax calculator
A simple and quick way to calculate your tax bill that's officially recognised by HMRC. Calculate and file your tax return online, it's just £10 for Which? members, and £36 for non-members.
Most UK taxpayers have tax deducted at source (via Pay As You Earn, or PAYE) and don’t have to fill in a tax return.
However, more than 10 million people need to complete a self-assessment tax return (SA100 or SA200), and submit this to their tax office.
You need to fill in a self-assessment tax return if:
- you're self-employed, a business partner, or director of a limited company
- you're an employee or pensioner with an annual income of £100,000 or more
- you have a pre-tax investment income of £10,000 or more
- you're a 'name' at the Lloyd's of London insurance market
- you're a minister of religion
- you're a trustee or representative of someone who has died
It's also worth noting that you're legally obligated to fill in a self-assessment tax form if you receive one.
- The more you delay, the more you have to pay
- If you fail to pay, the situation will worsen as you'll also be charged interest from the date the payment is due
- There are circumstances which would be seen as a reasonable excuse for filing your tax return late - but remember each case is taken on individual merit
Reasonable excuses for filing late
HMRC may waive the penalty for a late return if you can provide a 'reasonable' excuse.
On its website HMRC states that a reasonable excuse for missing the deadline is 'normally something unexpected or outside your control that stopped you meeting a tax obligation'.
- the recent death of a partner
- an unexpected stay in hospital
- computer failures
- service issues with the tax authority’s online services
- a fire which prevented the completion of a tax return or postal delays
However, please remember that each case is unique and will be considered on its own merits.
These excuses only apply if the problem actually prevented you from filing your return on time. It's always best to file your return in plenty of time.
Online and paper returns
If you miss the paper deadline for returning your form to HMRC, do not send it off late because you will be fined.
If you have missed the paper deadline, you can complete your return online using the unique taxpayer reference (UTR) that HMRC will have given you.
What you mustn't do is submit a paper return late, even if it is before the online deadline.
You also cannot submit a paper return late and also complete an online tax return, thinking it will cover you.
If you have reason to complain to HMRC about poor service, use our guide.
Tax penalties and fines
If you miss the 31 January deadline, the longer you delay, the more you'll have to pay.
This includes submitting your paper tax return before the online deadline of 31 January, but after the paper deadline of 31 October.
So if you miss the paper deadline, it's best to go online to complete the form before 31 January instead.
If you don't, you could be subjected to the following penalties:
- One day late You'll automatically receive a £100 fine. This applies even if you have no tax to pay or have paid the tax you owe
- Three months late A fine of £10 for each following day up to a 90 day maximum of £900. This is in addition to the fixed penalty above, so the overall fine could be £1,000
- Six months late A fine of either £300 or 5% of the tax due, whichever is the higher. This will apply on top of the penalties above
- 12 months late Another £300 fine or 5% of the tax due, whichever is the higher, will be added to your bill on top of the penalties above.
In serious cases, if you're more than 12 months late with your tax return, you may be asked to pay up to 100% of the tax due as well as any tax you owe, doubling your payment
Late payment penalties
If you don't pay on time, you’ll be charged interest from the date the payment is due.
The HMRC’s website provides a calculator which helps you estimate your penalty for late self-assessment payment.