The majority – 3.5m people – will receive a rebate, typically of between £250 and £500, while 2m people have under-paid tax with the average amount owed between £400 and £500.
Workers who need to repay tax will see the outstanding amount collected in the 2013/2014 tax code but if this is not possible they will be asked by HMRC to make a direct payment. Employees who are owed money will receive cheques in the post within 14 working days.
The first letters were due to arrive this week and will continue to be sent out until the end of year reconciliation process finishes in October.
Keith Thomson, director of Dundee-based Blackadders, said: “There is no telling whether HMRC will get its records right on PAYE and with the best will in the world, tax planning can’t protect against those mistakes.
“In the past two or three years individuals who’ve changed jobs have had a particularly difficult time with tax. Consulting an adviser would be wise because not only do we see the whole picture, but we’re up to date on all the latest tax changes that may elude clients.”