According to HM Revenue and Customs (HMRC), an average of £379 will be given back to those who are owed a rebate in the coming weeks, while 1.6 million workers will be sent a bill for not paying enough tax.
Those who have underpaid are expected to cough up £537 on average as a result of the Pay As You Earn (PAYE) amendments for the new tax year which began last month.
Bills and rebates are due to be given out two months earlier than last year, which means that workers will be repaid faster and will also know the exact amount they owe more quickly.
Taxpayers are divided into tax codes depending on how much they earn, so that HMRC can deduct the right amount of tax at the source.
Workers can pay too much or not enough tax as a result of them not notifying the Government department of changes in their working lives.
It's thought that the majority (85%) of people in Britain pay the right amount of tax throughout the year, but the changes made at the end are for the 15% who pay more than they should or who don't pay enough.
To work out how much tax you should be paying check out this guide.