Check Your Tax Code! You May Have Overpaid Tax

Oh, tax codes! How I used to loathe them when I first started training to be a tax advisor. They can be fiddly little things. If you get them wrong, the consequences can be quite severe. Your client might end up overpaying or, even worse, underpaying tax and at the end of the year be left with a large tax bill. As you can probably imagine, that client won’t be a happy bunny.

I am a trainee tax advisor working in a small tax consultancy near London. Having arrived in London from Germany 8 years ago for a gap year adventure, I could not have imagined that one day I would end up becoming a UK tax advisor. Nowadays, I cannot imagine a better job for myself.

For most of us, having an incorrect tax code means that we end up overpaying tax. You have probably heard or been warned of the dangers of having an emergency tax code. Guess what? The emergency tax code – 1000L in 2014/15 – is the code most of us have to ensure that we pay the correct amount of tax.

A tax code tells your employer how much money you can earn tax free each year so that they can deduct the right amount of tax from your pay. For most of us, this will only be our basic personal allowance which is £10,000 for the 2014/15 tax year. The tax code itself is your tax free earnings divided by ten and followed by a letter (mostly “L”) – hence the tax code 1000L. Unless you have additional earnings or untaxed income, this code will ensure that you get your full personal allowance and that roughly the correct amount of tax is deducted from your pay.

So what are the “dangerous codes” to watch out for? Basically, any code that is not 1000L requires a proper check. Below I have listed a few common ones:

1000L W1/ M1

W1/ M1 means week 1/ month 1. Normally, your tax position is recalculated every time you are paid taking into account your total income for the year to ensure that you receive your full personal allowance over the course of a tax year. However, if your employer uses a W1/ M1 code, they do not have enough information about your income before you started your job in order to calculate your personal allowance for the remaining tax year. Instead, you are given 1/12 or 1/52 of your personal allowance (depending whether you are paid monthly or weekly). However, this may not give you your full personal allowance if, for example, you had a lower or no income before you started your job and you may end up overpaying tax.

The W1/ M1 code is meant to be a temporary one and should be amended by HMRC. However, if this does not happen, you may want to call HMRC on the taxes helpline (tel: 0300 200 3300) and ask for it to be amended.


If your tax code is 0T, alarm bells should ring. Your employer will use this tax code if you do not complete a starter declaration before you start your job.

When you begin a new job, in certain circumstances your employer may ask you to make a starter declaration to find out whether you had any employment or benefits income before you started your job or whether you have another job.

The 0T code will not give you any personal allowance and deduct tax at the respective tax rates. If you have such a code, you will almost inevitably be overpaying tax and should ring HMRC to request for it to be amended as soon as possible.

BR, D0 or D1

You are most likely to come across a BR code. This code deducts tax at a rate of 20% (D0 deducts tax at 40% and D1 at 45%). If you have a second job, this job is likely to have a BR code with the 1000L code being allocated against your main job. However, if you earn less than £10,000 per year in your main job, the 1000L code will not give you your full personal allowance. The unused part of the allowance should be transferred to your second tax code as otherwise you end up overpaying tax.

Other codes

Sometimes tax codes can be more complicated, for example if you have other untaxed income, are entitled to a higher personal allowance, receive benefits from your employer (e.g. private medical insurance or a company car) or incur job expenses. Your tax code must contain all your untaxed income and allowances for the correct amount of tax to be deducted. If you are unsure whether your tax code is correct, you may want to get advice from HMRC on the taxes helpline.

Where can you find your tax code?

You may have received a tax coding notice from HMRC prior to the beginning of the tax year. However, not everybody gets such a notice. If you recently stopped working and received a form P45 from your employer, you will find your tax code on that form. (An employer must provide a P45 to any employee that stopped working for them). Alternatively, you can ring up the HMRC taxes helpline to find out.

If you had a wrong tax code in the past

The standard tax codes in the past 4 tax years were as follows:

2010/11: 647L
2011/12: 747L
2012/13: 810L
2013/14: 944L

If you are concerned that you may have overpaid tax in the past due to an incorrect tax code, you can make a claim for repayment of tax for up to the past 4 years.

It has been a year since I started working in tax and I’m still not a big fan of those tax codes. However, luckily for most of us, our tax codes are likely to be quite straight forward. However, they are well worth checking as, if they are wrong, you may end up paying the wrong amount of tax. And who knows, you may discover that you have overpaid tax and can claim a refund.

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