3 times a prenup is non-negotiable, according to a financial planner

A financial planner says that they're essential for anyone with a family business on one side of the marriage, for second marriages with children involved, and for anyone who has a large disparity in assets.
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Getting a prenuptial agreement isn't often the first thing on many couples' minds after they decide to tie the knot. But, in some scenarios, it can be an essential.

Ylisa Sanford , an Ameriprise private wealth adviser and financial planner, says there are a few reasons couples need one.

"From a financial planning standpoint, I think that they're very effective," Sanford says. While she admits that the idea can be unromantic, the principles behind them are simple: It's a protection. Sanford likens them to car insurance: "I'm not planning to have a car accident, but I have insurance in case," she says.

In her experience, there are a few situations where there's no question on whether or not a prenuptial agreement is needed.

1. Second marriages with children call for a prenup

Situations that involve several families merging into one can make for complicated money discussions down the road.

Especially when two spouses already have children coming into the marriage, a prenup is essential. "One of the most common scenarios is where you've got a second marriage. The premarital agreement will stipulate yes, the remaining spouse will get the assets if one of the spouses die," Sanford says.

As an example, she points out that unintended family members could end up with a spouse's money if it's not laid out correctly in a prenup. "Let's say spouse A has two kids, and spouse B has two kids. Spouse A's money goes to spouse B once spouse A dies. But, when spouse B dies, that money should go back to spouse A's kids, not to spouse B's kids."

A prenuptial agreement could help these sorts of transitions go smoothly, even when couples married a second time do stay together. "It's very effective and cuts out confusion, frustration, and disharmony," Sanford says.

2. If one partners family owns a business, a prenup is a safety net

Sanford says that any couple who has a family business involved should probably play it safe and opt for a prenup.

"If there's a family business involved, you don't want a situation where there's a marital dissolution and a multi-generational family businesses is having to be split to go to an ex-spouse," she says.

Things like your family's business and even any intellectual property rights you own can be included in prenups, and can help protect a business as well as assets if you ever do need to go your separate ways.

3. A disparity in assets can make a prenup essential but it doesnt have to be huge

When one partner has more assets than the other, Sanford says, a prenup is essential. But, you don't have to be a millionaire; even the typical person who has started investing or owning real estate before they're married could benefit.

Prenups are gaining popularity with millennials , and the fact that many are marrying later and starting their financial lives before marriage might be why.

"Millennials have been on their own, accumulated some wealth, either from a 401(k) or a stock program provided by their employer or some real estate, and they want to make sure that the property remains theirs if there are problems down the road," Leanna Johannes, a senior wealth strategist at PNC Wealth Management previously told Business Insider.

A financial planner can help you decide if a prenup is the right move

Working with a financial planner and the right professionals can help you determine whether a prenup is right for your situation and your relationship.

"In certain cases, they can take on a life of their own if people get too emotionally invested in them," Sanford says. "But, premarital agreements that are structured fairly and ethically by parties that have had proper consultation can make things very easy if there's a dissolution."