This way you and your partner can work through any potential financial issues or help one another budget individually or as a family.

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If you add a domestic partner to your policy, you must pay income taxes on the portion of the premium for your partner that your employer pays. (By contrast, you aren't taxed on benefits for a legal spouse or children.) So if your partner has insurance through his or her company, it's probably best to keep the two separate policies.

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But there are other reasons: you could be a beneficiary of a trust or estate or a shareholder or partner in a pass through entity and just now getting your Schedule K-1.

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