Child benefit and maintenance
If you or your partner receive Child Benefit, and your income exceeds £50,000 then you may have to pay a High Income Child Benefit Tax Charge. You will also be required to file tax returns even if you just earn a salary. The obligation falls on the higher earning partner, even if they're not the one who receives the benefit.
The charge effectively pays back some of the benefit you or your partner have received. Each £100 you earn you'll pay back 1% of the benefit. So if you earn more than £60,000 then you have to pay back all the money you received. In this case, you can choose not to claim Child Benefit (and won't need to file a tax return just because of this). However it means you may miss out on the benefit counting towards your national insurance contributions for your pension.
The charge will be added to the tax that you pay at the end of the year.
To make this easy in untied, there is a box to indicate if you receive Child Benefit - this appears when you file your return.
Child maintenance does not need to be included on your tax return for either the payer or the recipient.
(Strictly, there are ways to get some relief. You need to have been born before April 1935, and still have a young child. If this is you, let us know.)