For example
Katya and Leroy have a baby. Katya is staying at home to look after the baby. Leroy earns £51,000 a year. Leroy has to pay extra tax to repay some of their Child Benefit. His income is 10 x £100 over the limit, so the extra tax is 10% of their Child Benefit of £20.70 per week. He pays extra tax of £107.64 a year.
You still get paid the full amount of Child Benefit each month (or each week if you’re paid weekly). However, whichever one of you has the higher income has to pay back the full amount in the form of Income Tax.
You need to fill in a Self Assessment tax return so that HM Revenue & Customs (HMRC) can calculate the extra Income Tax you have to pay.