Martin Lewis is urging all workers to check their tax code after the first pay packet of the new financial year. The finance guru said it is important to check to make sure that you are not being overcharged by the tax office. If you have had a pay slip since 6 April you should make sure that you are on the right code, as you may be entitled to claim some money back. Why do I need to check my tax code? If your tax code is wrong you might be able to reclaim cash you have overpaid, or it could show whether you are underpaying tax. Your tax code might be wrong if you have recently changed jobs or if you have more than one income. It can also be affected if part of your salary is made up of company benefits, such as medical insurance or a company car. People who have just started their first job are often put on an emergency tax code and will wrongly be charged a higher rate. How can I check I’m paying the correct amount of tax? You can use MoneySavingExpert’s free tax code calculator to make sure you’re paying the correct amount. If you know your tax code, enter it into the calculator to find out how much you should be paying to the tax office. Workers who are unsure what code they should be on can look at their payslip, P45 or P60 form, or ask your human resources department for these if you do not know where to find them. If you have just one employer and earn under £100,000, your code is likely to be 1257L. How can I claim back overpaid tax? If you have been charged too much tax you should be able to get a refund, but the rebate method depends on when the extra was paid and your current work situation. For example, if you are owed a rebate from your current job from 6 April 2022, you will get the money back in your pay when your tax code has been corrected. You can call HMRC (HM Revenue and Customs) on 0300 200 3300 to change your tax code. If the overpayment was between April 2021 and 2022, HMRC will post you a P800 tax calculation, explaining how to get a refund. Workers who paid extra tax between April 2018 and 2021 will have to apply for a rebate online. If the overpayment was made before April 2018, you will not be able to get the money back.