<prompt> Human: Background: My girlfriend is thinking about accepting a contract position and since there wont be any benefits, Im considering adding her to my insurance as a dependent. We are not yet married, but will be in 2019. She does have her own place right now, but stays over at my place 6 days a week. Looking at the requirements of adding her as a dependent, it appears she can be listed as a domestic partner as long as we meet the following criteria, which we do - You live together in an exclusive, committed relationship, identical to being married:Live together means that you share the same living quarters. You will not be considered to have stopped living together if one of you leaves the shared quarters for a period of time but intends to return. Exclusive means that your partner is your sole domestic partner. Committed relationship means that the relationship is intended to last indefinitely and that you and your partner are responsible for each others common welfare. Both of you must be at least 18 years old and mentally competent to enter into a contract. Neither of you is married to another person. You and your partner are not related in any way that would prevent a marriage in the state in which you reside. Neither of you has been in a previous domestic partnership within the previous six months Since Ive never done this before, is there anything I should watch out for in terms of potential tax implications? I currently have 1 allowance on my W4 and have always been filing as Single - would I need to change this? Thanks in advance!EDIT We are both in California, if that matters. Shes currently renting and I own a townhouse.Assistant: No real tax implications but HR is going to fight you tooth and nail on this, especially since she technically has her own place.EDIT: Also, DO NOT CHANGE YOUR W4. This is going to have the opposite effect you think - it will cause them to withold less taxes as if you were married or had a dependent for tax purposes which you do not. You will file taxes the same as you have previously until you are legally married. Human: Is there a reason for that? I would be paying more to add her on. Im currently on the Kaiser HMO and am paying about 24 per pay period. Adding a domestic partner would increase that to 110 per pay period.  <response>: Because they are paying the vast majority of the premiums so adding her costs them quite a bit of money. Also, this isnt really the way this carve out was designed to work. They really intend it for same sex partners that previously couldnt get married as opposed to cohabiting couples. You are presumably in the right here because they are the ones that wrote the policy but just know that it is likely you are going to get pushback when you go in and say you want to add your girlfriend to your insurance. 