A Martin Lewis fan has explained how they got £9,400 back from the tax man by doing a simple check.
The MoneySavingExpert reader had been on the wrong tax code for three years due to an error by her employer.
She said her boss hadn’t updated her tax code - meaning she had been overpaying to the tune of thousands of pounds.
"It took an hour on the phone to HMRC, but I've now been refunded £9,400," she told MoneySavingExpert.
The success story was shared in the latest MSE weekly newsletter - but the money-saving website estimates millions more workers could also be on the wrong tax code too.
This means you could also be owed be thousands of pounds in overpaid tax.
How to check your tax code
You tax code is made up of numbers and letters. It tells your employer or pension provider how much you can earn before you start being taxed.
The most common code for the current tax year is 1257L for people who have one job or pension - although not everyone will be on this.
If you're on this tax code, it means you can earn £12,570 before being taxed in the 2021/22 tax year.
There are several ways you can find your tax code - the simplest way to check is to look at your latest payslip, or on your P45 if you have recently quit your job.
You can also ask your HR department if they can tell you your tax code.
The Gov.uk website has a dedicated webpage where you can see your tax code as well - to check it online, you will need to register for a government gateway ID.
When it comes to checking if your tax code is correct, MoneySavingExpert has a free tax code calculator that you can use to get a rough idea as to whether yours is right.
You'll need to enter your earnings before tax and your current code, and the calculator will then tell whether you are likely on the right code.
No tax calculator will be able to tell you for definite if you are on the right code - but this should give you a good indication.
How to claim back tax if you've been overpaying
If you suspect you’re on the wrong tax code, you can contact HMRC and ask them to investigate.
You can call HMRC on 0300 200 3300, or speak to a customer service member or staff online via their live chat service.
If your tax code is wrong for the current tax year, HMRC will contact your employer to correct it. You should then get back any owed tax in your next payslip.
If you have been overpaying tax for some time, you can claim back up to four additional years. This means you can go back as far as the 2017/18 tax year.
Have you managed to get thousands of pounds back from the tax man? Let us know: levi.winchester@reachplc.com
It is still worth flagging to HMRC if you think you’ve been overpaying for longer than this though.
Workers who are investigating their tax code may also find they’ve been underpaying tax - in this case, you would owe HMRC money.
It is better to sort this out sooner rather than later to avoid having to pay back a larger sum.
You can try and get the tax written off if it was not your fault that you underpaid - but this is not a guarantee.
You can do this by asking for a so-called "Extra Statutory Concession" or an A19 from HMRC.
