A guide to prenups - and what happens when super rich couples don't have one

• Bill and Melinda Gates reportedly did not sign a prenup, but did sign a "separation agreement."
• A prenup protects individuals' assets they enter the marriage with, and gain over the course of it.
• While all income levels can benefit from one, the richest have more to lose if they forgo a prenup.

Bill and Melinda Gates did not sign a prenup, TMZ reported Monday, or a legal agreement signed before marriage that stipulates how assets - from homes to businesses - are to be divided in the event of a divorce or death.

The philanthropic power couple announced their split Monday after 27 years of marriage.

While people of all incomes levels can benefit from a prenup - for instance, young couples may want one to protect themselves from taking on their partner's student debt - the richest stand to lose a lot more should they forgo one.

And the Gateses are the richest of the rich: Microsoft cofounder Bill Gates is worth an estimated $146 billion, according to Bloomberg, and the couple's foundation had net assets of $43.3 billion at the end of 2019.

A prenup can cover 'comingled' assets that add up over the course of a marriage

Signing a prenup first involves spouses-to-be to put all their cards on the table, revealing how much money they have and property they own, according to the NYC Bar. Then, they set their own terms for how to divide it in the event of divorce or death, rather than leave it up to the state.

The pair can also use a prenup to agree upon how they'll share (or not) finances during the marriage.

A prenup can also address the wealth a couple stands to gain over the course of their marriage. Russell D. Knight, a divorce lawyer in Florida, told NBC's Better these "comingled" assets are complicated, and common.

"Buying a house together with just one person's money is commingling. Starting a business together using one person's capital is commingling. Moving money around more than a few times can even qualify as commingling," he said. "The longer you've been married, the more you are likely to commingle your assets [and have] non-marital assets turn into marital and, thus, divisible assets."

Bill and Melinda Gates do have a 'separation contract,' TMZ reported

A separation contract is a private legal document signed by a couple when they want to live apart. It lists their rights and obligations, such as child support and custody, and doesn't involve the court, Insider's Grace Dean reported.

The Gateses' separation contract reportedly stipulates how their physical property, personal property, and debts will be split. Melinda Gates did not ask for spousal support.

It's unclear how having a prenup instead would have changed their division of property, although a prenup (or postnup, an alternative that couples sign after marriage) is necessary to keep state laws out of the equation.

Washington state, where the Gateses filed for divorce, is a "community property" state where all money earned and property bought during the marriage is considered equally owned by husband and wife, according to legal guide Nolo.

The wealthiest stand more to lose

If one member of a couple comes into the marriage exceptionally rich, or becomes wealthy during it, they have more to lose without the protection of a prenup.

Take Amazon Billionaire CEO Jeff Bezos, who divorced in 2019 and did not have a prenuptial agreement with his wife MacKenzie Scott. Their settlement was $38 billion, making MacKenzie Scott the world's third-wealthiest woman.