Between now and October 2012 around 5.1 million taxpayers will receive notice of a tax under or over-payment, arising from the PAYE reconciliation exercise for 2011/12. These PAYE adjustments are the natural result of calculating whether each taxpayer has paid the right amount of tax through PAYE or not.
The PAYE system does not cope well when a person has several employments or pensions running concurrently, or changes the benefits in kind (such as a car or medical payments) part way through the tax year. As a result the amount of tax deducted from salary or pension is not perfect, although more problems are being overcome every year.
When the HMRC computer calculates that you have under or over-paid tax for the year it will send you a tax calculation on form P800. We will not get a copy of the P800 as your tax agent, so if you want us to check the figures for you please send us a copy.
If you are going to check the tax calculation yourself, start with the forms P60 or P45 you have received from your pension provider or employer for the tax year. First ensure you are comparing documents for the same tax year, the latest P800 form should be for 2011/12, but you may be sent calculations for earlier tax years. Is all the tax deducted as reported on the forms P60 also shown on the P800? There have been cases of HMRC mixing up the PAYE records of two taxpayers, so watch for any discrepancies in your taxed income figures.
You also need to check that your full personal allowance has been included, and the amounts for benefits or other income are accurate. These figures are often estimated at the beginning of the tax year, and may not have been amended to reflect the true amounts.