We need to know the number of children you have (or are expecting) to calculate your entitlement to Child Benefit and Child Tax Credit.
In general the rules in benefits and tax credits follow the rules in Child Benefit. So if you (or your partner) are already claiming Child Benefit for a child then you should include them in the calculator. Only one member of the family can make a claim for each child, though on occasion one parent claims Child Benefit for a child and the other claims Child Tax Credit for them.
More information is available on the rules for Children between 16 and 20 and on Children born/adopted recently or expected.
If you share custody of a child it is the person with 'main responsibility' who is normally eligible to claim Child Benefit and Child Tax Credit.
When deciding who has main responsibility for a child, the number of days the child lives with you is important (the 'normally living with' test). However this is not the only factor that HM Revenue and Customs consider. For Child Tax Credit the 'normally living with' test can be considered on a more flexible basis than for Child Benefit. See HM Revenue and Customs advice on shared custody.
Care and adoption
If you have a child who is in care or you are caring for or adopting a child, then special rules apply to both Child Benefit and Child Tax Credit. You should ask HM Revenue and Customs how the rules affect you.
Rules in out-of-work benefits
People making a new claim for means-tested out-of-work benefits (Income Support, Jobseeker’s Allowance and Employment and Support Allowance) now have additional amounts paid for qualifying children through Child Tax Credit. The calculator works out entitlement to out-of-work benefits on this ‘adult-only’ basis. For more information see child additions in Income Support and JSA.
If you claim Child Benefit for a child aged 16 years or over who is sick or disabled you may instead be better-off if they claimed Employment and Support Allowance. For more information see Employment and Support Allowance in youth.