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How do I file a Self Assessment tax return quickly?

  • 5 min read
  • Last updated 24 Mar 2023

If you’re not sure how to do a Self Assessment tax return, don’t panic. It’s not as horrifying as it might seem – and there are ways to get it sorted speedily. Before anything else though, work out why you need to file:

  • You’re a landlord earning rental income
  • You earn over £100,000
  • You’re self-employed
  • You have side-gigs alongside your full-time job
  • You’re an investor with profits that exceed the tax-free allowances
  • You earn over £50,270 and want to claim additional pension relief

What is Self Assessment?

Self Assessment is basically the way that you declare and pay your taxes to HMRC. You tell them about your untaxed income and they calculate the bill you owe. You can file your Self Assessment online or by paper; for speed and ease (and because we’re TaxScouts), we’d recommend online. 

If you file by paper, you’ll need a Self Assessment tax return form called the SA100. There are more forms to complete based on the reason you’re filing. Read more about what Self Assessment tax form you need to be able to file your return on paper.

Never miss a tax deadline

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How do I do a Self Assessment online?

This is markedly easier. The online tax Self Assessment deadline is not only later than the paper one, but you don’t have to navigate piles of paper admin. So, project file Self Assessment: where do you start? 

We’d recommend getting all your income and expenses onto a spreadsheet so you can work quickly with your totals. If you don’t already have a UTR number, register for Self Assessment ASAP because you won’t be able to file without one. From here, you can log into HMRC online with your government gateway ID and go through their online form.

(What the heck is my government gateway ID and how do I find it?)

But how do I do the Self Assessment tax return?

This depends on what type of tax return you need to do, and whether it’s online or on paper. Also, the more reliefs you’re claiming and the more complicated your return, the harder it can be to do it on your own. 

If you’re self-employed and become pregnant, for instance, you may start claiming the Maternity Allowance which will affect the calculations on your tax return. 

The margin for error is slim with HMRC. Getting Self Assessment help may well be worthwhile – but we would say that as a fine purveyor of the Self Assessment tax return online, right? 😏

When do I do the return?

There are two dates to bear in mind. 

If you’ve never done your tax return before, you will need to register for Self Assessment first. This is how HMRC knows that you are earning untaxed income. You should do this by 5th October in any given year. 

When it comes to paying your tax return, the Self Assessment deadline is 31st January the year after the tax year you’re paying for. If you’re paying your 2023/2024 tax return, this should be paid by 31st January 2025.

Make sure that you do this on time. Doing either of these things late will incur penalties.

Tax reliefs for landlords

If you’re a landlord, there are a few things to consider when you do your tax return:

  • Do you live in the property that you’re renting out?
  • Do you own the property you’re renting out?
  • How many properties do you have?

If you’re only renting a room in the property you own, you’re covered by the Rent-a-Room scheme. You can earn up to £7,500 per year tax-free. Anything over that you’ll pay Income Tax on. If you don’t live in the property, you can claim the Property Income Allowance which gives you £1,000 of your rental income tax-free. You can also claim a 20% tax relief on mortgage interest. If you’re using the Rent2Rent scheme, the same rules apply as if you owned the property.

Read more about tax owed on rental income here.

Tax reliefs for self-employed work

If you’re self-employed, you only pay tax on income over the £12,570 Personal Allowance. You are also allowed to deduct your business expenses from your earnings. 

If you do side gigs alongside your full-time job, you can make the most of the Trading Allowance which allows you to earn up to £1,000 additional income, tax-free. Beyond this, you must do a tax return at the usual rates of Income Tax and National Insurance.

Check out our Self Assessment calculator for the self-employed 👇

Your situation

Outlined number oneOutlined number one
I am
Annual self-employed income
Self-employed expenses

Tax and profit

Outlined number two
  • Total earnings
    £1,000 tax-free Trading Allowance
  • Tax to pay
    £7,286 income tax
    £159 class 2 National Insurance
    £3,549 class 4 National Insurance
  • What you’re left with

How your income tax is calculated

When you’re self-employed, you have to pay your income tax and national insurance contributions yourself in your annual Self Assessment. Our calculator helps you quickly assess how much you owe.

However you may be eligible for a tax refund when:

  1. You already made tax payments for the year but your annual income ended up less than planned
  2. You have done things that qualify for a tax relief (made private pension contributions, given to charity, etc.)

In your case when you earn £50,000:

Income tax breakdown

You pay no income tax on first £12,570 that you make

You pay £7,286 at basic income tax rate (20%) on the next £36,430

National insurance contributions breakdown

No contributions on the first £9,568 that you make

You pay £3,549 in contributions (at 9%) on the next £39,432 that you make

You pay £159 in NI Class 2 contributions

I earn over £100,000

When you earn over £100,000, you’re classed as a high earner. Therefore, even though you pay your taxes through your salary, HMRC needs to check your income to ensure that you’re paying the correct amount of tax. To do this, you need to do a tax return.

But as a high earner, you can end up paying up to 60% tax! However, there are ways to reduce this. Read here to see how.

I’m an investor

To pay tax on your profits, you should pay attention to Capital Gains Tax rates. The Capital Gains Tax Allowance in the 2023/24 tax year is £6,000. This means that any profits earned that are less than this are tax-free. There are other factors that affect the tax you owe on any investment profits, such as carrying forward losses, but it can all get a little bit complicated.

To make it simple, we have a Self Assessment tax calculator specifically for Capital Gains Tax. We’ll help you work it out.

Your situation

Outlined number oneOutlined number one
How did you make money?
Profit from capital gains
Annual salary
Other income

Tax and profit

Outlined number two
  • Your profit from
    Incl. £12,300 tax-free CGT allowance
  • Capital Gains Tax to pay
  • Profit after tax

How your capital gains tax is calculated

Your total capital gains tax (CGT) owed depends on two main components:

  1. How much you earn in total
  2. What type of assets you sell

Your overall earnings determine how much of your capital gains are taxed at 10% or 20%.
Our capital gains tax rates guide explains this in more detail.

In your case where capital gains from shares were £20,000 and your total annual earnings were £69,000:

Capital gains tax (CGT) breakdown

You pay no CGT on the first £12,300 that you make

You pay £127 at 10% tax rate for the next £1,270 of your capital gains

You pay £1,286 at 20% tax rate on the remaining £6,430 of your capital gains

How to pay Self Assessment Tax

Paying your tax bill is simple. Make sure you do this by the Self Assessment tax return deadline on 31st January. You can pay by Direct Debit, by bank transfer, with a paying-in slip, with your debit card, or by cheque. 

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