If you live with a partner you should enter that you are part of a couple. It does not matter whether you are married or living together, or whether you are an opposite-sex or same-sex couple.
The meaning of 'couple' in the benefits and tax credits system is the same as in everyday speech. People who are living together in a relationship count as a couple for assessing their benefits and tax credits. If your situation is more complicated you should seek advice.
The rules for benefits and tax credits apply to people who are living together as a couple in a relationship and not to people who are flat sharers or carers.
Before December 2005 the law treated same-sex couples and opposite-sex couples differently. Same-sex couples were treated as individuals and opposite-sex couples were treated as one claim. However, these rules now apply equally to same sex and opposite sex couples. Whether or not you are registered civil partners/married. If you live with a partner you should enter that you are part of a couple.
If you are in a couple you need to put in one claim form, giving details for yourself and for your partner. As a member of a couple, the income, savings and hours of work of both of the couple are taken into account.
In couples the calculator assumes that the first person referred to ('you' or 'client') claims the benefits. If you are both eligible to claim an out-of-work benefit you should consider carefully which one of you should make the claim. For more information see couples and out-of-work benefits.
If you are in a polygamous marriage you should seek further advice on your benefit entitlement.