Do I pay HICBC if my new partner claims Child Benefit for their children?

Does it matter that the children are not mine?

On the GOV.UK overview, no. The charge may apply if you or your partner receives Child Benefit and at least one of you has adjusted net income over the threshold. The same page says: it does not matter if the child living with you is not your own child.

A second official route: the charge may also apply if someone else gets Child Benefit for a child living with you and they contribute at least an equal amount towards the child’s upkeep. That is a different fact pattern from a new partner who already claims for children they brought into the household.

GOV.UK partner wording: someone you are not permanently separated from who you are married to, in a civil partnership with, or living with as if you were. A new relationship without living together as partners is not the test on that page.

From which date can the charge apply after they move in?

The circumstances-change page says the charge applies from the date you move in together until you permanently separate or Child Benefit stops. LITRG walks through whose weeks count: if you are the higher earner and your new partner is the claimant, the charge often uses only the Child Benefit from the weeks after you became partners, measured against your full-year adjusted net income.

How do I check this if I never claimed Child Benefit myself?

1. 1
   Confirm you live together as partners on the GOV.UK definition Married, in a civil partnership, or living together as if you were, and not permanently separated. Weekend stays without that living-together test are not what the overview describes.
2. 2
   Confirm someone is receiving Child Benefit in the household Your partner’s claim for their children is enough on GOV.UK’s wording. You do not need to have claimed, and the children do not need to be yours.
3. 3
   Work out each person’s adjusted net income for the whole tax year Follow adjusted net income. A December move-in does not let you annualise only the months you lived together.
4. 4
   If they will not share figures, write to HMRC for yes or no The Self Assessment and PAYE pages say you can ask whether a partner or ex-partner gets Child Benefit or has a higher income than you. HMRC replies yes or no. It will not give their financial information or National Insurance number. You can only ask if you live together, or separated within the tax year you are asking about.
5. 5
   Estimate on the official calculator, then pick PAYE or Self Assessment Use the Child Benefit tax calculator. Pay through PAYE only while that route is still open; otherwise register for Self Assessment. See the deadline article if you have never filed a return.

What will HMRC actually tell me about my partner’s claim?

Only yes or no. Write to Pay As You Earn and Self Assessment, HM Revenue and Customs, BX9 1AS, with the tax year, your name, address, date of birth and National Insurance number, your Unique Taxpayer Reference if you have one, your adjusted net income, and your partner or ex-partner’s name. Include their address, date of birth, National Insurance number and UTR if you know them.

That letter does not replace the calculator. It only answers whether they claim, or whether their income is higher than yours — the two facts GOV.UK says HMRC will confirm.

In shortIn short: a higher earner who never claimed can still owe the charge on a new partner’s Child Benefit from the weeks you live together as partners. The children do not have to be yours. HMRC confirms yes or no, not their numbers. Use the official calculator before you file or change a tax code.