If you have a life partner but no marriage certificate (or a legally recognized civil union or domestic partnership), estate planning is a must. Without it, neither of you will inherit from each other—and neither will have a say in the other's end-of-life medical care.

If you die without a valid will, state law will dictate where your solely owned property goes after your death, and it won't go to an unmarried partner. Instead, your children (if you have any) would inherit first, followed by your closest relatives, including your parents. Similarly, only your spouse or someone you've appointed in a valid health care power of attorney is allowed to make medical decisions on your behalf if you're incapacitated. Fortunately, you can create the legal documents you need yourself (or have an attorney draft them for you).

Write Your Wills

If you have some assets you care about, you should write a will, so you can leave your property to the recipients you choose, such as your partner, friends, or charitable organizations. If you don't write a will and do not have children, much of what you leave behind will likely go to your parents or siblings, under your state's laws. (Every state has intestate succession statutes, which list the relatives who inherit from someone who dies without a will.)

If you have young children, the other important reason for writing wills is to name a guardian for them. The guardian would raise the children if neither parent were able to. In that situation, the court would appoint someone as guardian. Unless there were a serious problem with the person the parents named in their wills, that's who the court would appoint.

If both you and your partner are legal parents of the children, then you'll want to name someone else as personal guardian, because a guardian won't be needed unless both parents are unavailable. If just one of you is a legal parent, you can name the other partner as the guardian. You might also want to write a letter, along with your will, to explain to the court why it's important for your partner to be the children's guardian. But be aware that if there's another legal parent in the picture, that person would probably take over raising the children.

Writing a simple will isn't difficult or expensive. Many people are comfortable doing it themselves, with an online app or software. (Try Nolo's bestselling Quicken WillMaker & Trust.)

Try Using a Living Trust

You also can leave assets to each other with a living trust; the trust performs the same function as a will, but lets the surviving partner avoid the hassle and expense of probate. Trusts also can be more flexible than wills. Most people don't make a living trust until they’re middle-aged or older.

Own Assets Together

Another way to make sure that neither of you is left out in the cold after the other dies is to own big-ticket items, such as houses and cars, together in joint tenancy with right of survivorship. That way, when one of you dies, the survivor automatically owns 100% of the property.

To do this, you'll need to put both of your names on the asset's official title document—for example, your car's certificate of title or the deed to your house. In most cases (depending on your state’s laws), you’ll need to indicate on the title that you own the property as joint tenants with right of survivorship.

Designate Beneficiaries for Bank and Other Accounts

You and your partner might not want to share ownership of all your assets (for many reasons). And retirement accounts can't be shared. So you'll probably need other ways to make sure assets you own in your name alone get to your partner at your death.

Some of these valuable assets—bank, investment, and retirement accounts—may not pass through your will. All you have to do to leave them to the person of your choice is to ask for a beneficiary designation form from the bank or account custodian, and name the people you want to inherit the funds.

It's easy, and it doesn't cost anything. If you change your mind later, you can just fill out and send in another form, naming a different person as beneficiary. (Learn more about beneficiary designations for different kinds of assets.)

Make Living Wills and Durable Powers of Attorney

You need these documents to give your partner authority over financial and medical decisions, in case it's ever necessary for someone to step in and make decisions on your behalf.

Use durable powers of attorney (DPOA) for finances to give each other authority over your assets. This can be a big benefit if either of you is ever unexpectedly struck by illness or injury. You might need quick access to your partner's checking account to pay the mortgage, for example. Without a DPOA for finances, you would have to go to court and prove that your partner was incapacitated and that you should have control over your partner’s assets.

Make durable powers of attorney for health care to give each other the authority to make medical decisions for the other, if you're ever unable to make them on your own. Along with the health care DPOA, make a living will, in which you set out your wishes for end-of-life health care in as much detail as you choose. Many states combine the living will and health care DPOA into one document—often called an “advance directive,” “health care directive,” or something similar. Your doctors and other health care providers must follow your wishes, and putting them in writing lets your partner know what you want as well.

Getting Legal Help

Unmarried partners don’t have all of the rights that married partners have, so it’s important to ensure you and your partner’s wishes are met. It’s possible to create the above documents on your own. But, if you’re uncomfortable with legal documents, or have particularly complicated family dynamics, you can consult with an estate planning attorney licensed in your state. If you or your partner have significant assets that could trigger estate taxes, you should speak with an estate planning attorney.