Self Assessment online tax return 2025: deadline, how to file and more

The online Self Assessment tax return deadline for the 2023/24 tax year is midnight on 31 January.

Self-employed Brits will need to file their online Self Assessment tax return by midnight on 31 January.

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If you're required to file a Self Assessment tax return and miss the deadline, you will be hit with a £100 fine – even if you've done the sums and believe you have no tax to pay.

If you've still not paid after three months, HMRC will add an extra £10 every day, up to a maximum of £900.

After six months, you'll be hit with either a 5% charge of the tax you owed or £300, whichever is greater.

Another 5% or £300 charge will be added after one year.

That means missing a year's payments could see you saddled with total penalties worth upwards of £1,500.

That's obviously something everyone wants to avoid.

So how do you go about filing your online tax return? Here are our top tips to make beating the deadline as painless as possible.

We're not saying it's going to be fun, but it really needn't be too daunting.

Do you have a Gateway account?

Ideally, you'll already have registered to use HMRC’s online tax return service by now and are ready to start filling in forms.

It can take up to 10 days (or 21 if you live abroad) to sign up through the Government Gateway PIN verification system.

Once that's done, it’s time to tackle that return.

Here are some top tips to help make the process as painless as possible. But first, take a look at what documents you’ll need to fill out your Self Assessment form.

If you're looking to simply make a payment on account instead, here's all you need to know.

1. Don't have all your figures? Use (realistic) estimates

If you do not have exact figures, put in estimates. You must, however, make the estimates as accurate as possible, and clarify on the form that the figures are estimates and not exact.

You will still need to supply exact figures later, but at least estimates will do for now.

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2. Look for the best sources of information

Focus on the most relevant information. If you don't have a P60 form from your employer, your March payslip will have much of the same information.

Earlier payslips can be ignored. Your bank statements can also tell you much of what you need to know – how much you paid in pension contributions, charitable donations and so on.

3. Remember interest payments

Don't forget to declare the interest you received from your bank.

Your March statement will often show how much interest you received over the year, so that's the most important one to look at.

Common tax return blunders to avoid

4. And don't forget dividends

Similarly, you must declare the dividends you received from shares or similar investments.

This rule applies whether you received the dividends as cash or they were reinvested.

If you don't have a personalised dividend certificate, the fund manager or company will usually list the dividend paid per share on its website.

You can multiply that by the current number of shares you own to work out the dividend you received.

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5. Make sure you claim everything you're eligible for

While filing tax returns is never going to be fun, it's worth pointing out that there are loads of things you can actually claim for. These could be worth hundreds of pounds.

From additional pension tax relief to working from home rebates, we've listed all the things you might be eligible for here.

6. Ask questions now

Finally, remember that the internet and the phone are your friends. If you can't find the relevant paper statements, you may be able to get the info you need over the phone or online.

Remember that you will most likely face an automatic £100 fine if you miss the deadline without a valid excuse.

There are plenty of help sheets on the Self Assessment section of the Gov.uk website, or you can call the helpline on 0300 200 3310.

You'll need your Unique Taxpayer Reference (UTR) number to hand when calling.

You could also try getting in touch on Twitter anytime between 8 am and 10 pm.

However, please make sure you don't post any personal details as criminals have been known to use these.

Read: best ways to contact the taxman

7. Watch out for scams!

As a final point, be extremely careful who you hand your details over. HMRC will occasionally contact you by email or even text (depending on which details you've given them), for example, to remind you to fill out your tax form.

However, the taxman will never contact you via email or phone/text to tell you about a refund. This will always be done by post. Have a read of our guide to spotting tax scams in order to stay one step ahead of the crooks.

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