Prenuptial Agreements in South Dakota: Why Spousal Support Can't Be Waived

You are planning a South Dakota wedding, and somewhere between the venue deposit and the guest list, the word "prenup" has come up. Maybe one of you owns land near Brookings, or a business in Sioux Falls, or is walking into the marriage with student debt. You want to know whether a prenup even holds up here, what it can do, and what it will cost you without turning the whole thing into a legal ordeal.

The good news is that South Dakota makes this reasonably clear. The state adopted the Uniform Premarital Agreement Act, the same framework used in 29 states plus the District of Columbia, which spells out what a valid prenup requires. For context on why couples plan ahead at all, the CDC's National Center for Health Statistics reported about 2,041,926 marriages and 672,502 divorces across the 45 reporting states and D.C. in 2023 (CDC/NCHS FastStats). Planning for the good years and the hard ones is what a South Dakota prenup is built to do. Here is how it works.

Are prenups valid in South Dakota?

Yes. A prenup is valid and enforceable in South Dakota. The state's requirements are light on formality. Under SDCL 25-2-17, a premarital agreement must be in writing and signed by both parties, and it is enforceable without consideration, meaning neither partner has to give up something of value in exchange for signing.

Notice what that statute does not require. There is no notary requirement and no witness requirement for a South Dakota prenup to be valid. A written document, signed by both of you, is the baseline the law asks for.

That said, notarizing the agreement is still worth doing. A notarized signature is straightforward evidence that both partners signed, which is one less thing for anyone to dispute later. If you want to see how South Dakota's approach compares with other states, our guide on how prenuptial agreements vary across America lays out the differences side by side.

What makes a South Dakota prenup enforceable?

Meeting the writing-and-signature requirement gets you a valid agreement. Keeping it enforceable if it is ever challenged is a separate question, and this is where most of the care goes.

South Dakota courts look at how the agreement was signed, not whether it looks fair years later. Under SDCL 25-2-21, a prenup is unenforceable if the challenging partner proves they did not sign voluntarily, or that the agreement was unconscionable when it was signed and, before signing, that partner was not given fair and reasonable disclosure of the other's finances, did not waive that disclosure in writing, and did not otherwise have adequate knowledge of the other's property and debts.

A couple of those terms are worth unpacking. Unconscionable means a term so one-sided or unfair at the moment it was signed that a court considers enforcing it unjust. The test is anchored to the time of signing, so an agreement does not become unenforceable because one partner's finances later changed.

The practical takeaway is that two things protect a South Dakota prenup: full financial disclosure and voluntariness. Full financial disclosure means each partner lays out what they own and owe before signing, so neither can later claim they were in the dark. Voluntariness means neither partner was rushed or pressured. Signing early, with time to read and think, removes the argument that anyone was hurried into it. Our explainer on what makes a prenup enforceable goes deeper on both.

How does South Dakota divide property without a prenup?

If you skip a prenup, South Dakota's default rules decide who gets what in a divorce. Understanding that default is the clearest way to see what a prenup changes.

South Dakota is an equitable distribution state, not a community property state. Under SDCL 25-4-44, a court may make an equitable division of the property belonging to either or both spouses, whether the title is held by one partner or both, with regard for the equity and circumstances of the parties. Equitable division means a court splits property based on what is fair given the couple's circumstances, and "equitable" does not always mean "equal." A judge can weigh factors and land somewhere other than a clean 50/50.

The detail that surprises many couples is the reach of that statute. It applies to property belonging to either spouse, which can include assets a partner brought into the marriage. Without a prenup, the home you owned before the wedding or the savings you built on your own are not automatically off the table. A prenup is the tool that lets the two of you decide these questions in advance, rather than leaving them to a court's sense of what is equitable.

What can a South Dakota prenup cover (and what can't it)?

A South Dakota prenup can settle most of the financial questions a marriage raises. You can designate what counts as each partner's separate property and what becomes marital property. You can decide how property is divided if the marriage ends. You can assign responsibility for debts, so one partner's student loans or business liabilities stay their own. And you can address inheritance and what happens to property at death, coordinating the agreement with your estate plans. Our overview of what a prenup protects walks through these categories in more detail.

There are limits, and South Dakota has one that sets it apart from most states. A prenup here cannot waive or limit spousal support. In Sanford v. Sanford, 2005 SD 34, 694 N.W.2d 283, the South Dakota Supreme Court held that provisions purporting to waive or limit spousal support (alimony) are void as against public policy. So even in an otherwise solid agreement, a clause trying to eliminate alimony will not be enforced.

The useful part of that ruling is what it does to the rest of the document. The court treated the void support provision as severable, meaning it can be struck out while the valid property and debt terms continue to stand. Your agreement does not collapse because one clause is unenforceable; that clause drops away.

The other common limit is universal, not South Dakota specific: a prenup cannot decide child support or child custody. Those questions are governed by the child's best interests and stay with the court, regardless of what any agreement says.

How much does a prenup cost in South Dakota?

Cost is often what tips couples one way or the other, and in South Dakota the range is wide depending on the path you take.

The traditional route means each partner hires their own attorney. According to the Clio 2025 Legal Trends Report, South Dakota family-law attorneys charge about $276 an hour, with all-practice-area rates averaging around $252 an hour. Sioux Falls-area family-law rates run roughly $200 to $325 an hour. Because a prenup involves back and forth between two separately represented partners, the combined cost for a couple commonly lands somewhere between $2,100 and $8,100. For a broader look at what drives these numbers, see our guide on how much a prenup costs.

Here is how the paths compare:

South Dakota does not require either partner to hire a lawyer for a prenup to be valid. Some couples want that individual representation and choose to pay for it. Others want a straightforward, enforceable agreement without the hourly meter running.

How do you get a prenup in South Dakota?

The steps are more manageable than most couples expect. Start the conversation early, well before the wedding. South Dakota sets no waiting period, but signing as early as you reasonably can removes any later argument that someone was rushed. Next, each of you gathers a full picture of your finances: what you own, what you owe, and what income you bring in. Then you decide together how you want to handle property, debts, and inheritance, put those terms in writing, and both sign.

That is the whole shape of it. Because South Dakota law looks at the writing, the signatures, the disclosure, and the voluntariness rather than how the document was produced, an online prenup is a legitimate path here. An agreement built online that meets those conditions is enforceable the same way a lawyer-drafted one is.

This is where First fits. No hourly rates, no scheduling back and forth, no paperwork pile to manage. First gives couples in South Dakota a guided way to complete a prenup in South Dakota online, with the disclosure step built in and online notarization included, so the two things a court cares about most, honest disclosure and unpressured signing, stay in your hands.

Frequently asked questions

Are prenups enforceable in South Dakota?

Yes. South Dakota adopted the Uniform Premarital Agreement Act. A prenup must be in writing and signed by both partners. A court will enforce it unless the challenging partner proves they did not sign voluntarily, or that it was unconscionable when signed without fair disclosure, a written waiver, and adequate knowledge of the other's finances.

Does a South Dakota prenup have to be notarized?

No. South Dakota law does not require a prenup to be notarized or witnessed for it to be valid; it needs to be in writing and signed by both partners. Notarizing it is still worth doing, because a notarized signature is straightforward evidence that both partners signed.

How does South Dakota divide property without a prenup?

A South Dakota court may make an equitable division of the property belonging to either or both spouses, whoever holds the title, with regard for the circumstances of the parties. That includes property each partner brought into the marriage. Equitable means fair, which does not always mean an equal split.

Can a South Dakota prenup waive spousal support?

No. South Dakota courts have held that provisions waiving or limiting spousal support (alimony) are void as against public policy. That single provision can be severed from an otherwise valid agreement, so the property terms can still stand while the support waiver does not.

How much does a prenup cost in South Dakota?

It depends on the path. Hiring attorneys commonly runs $2,100 to $8,100 for the couple, because each partner needs their own and Sioux Falls-area family-law rates run about $200 to $325 an hour. With First, a South Dakota prenup is a $649 flat fee for the couple, with online notarization included.

Can I do a South Dakota prenup online?

Yes. Nothing in South Dakota law treats an agreement differently because of how it was produced. What matters is that it is in writing and signed, that both partners disclosed their finances fully, and that both signed freely. An online prenup that meets those conditions is enforceable the same way a lawyer-drafted one is.

Getting started

A South Dakota prenup is within reach. It needs to be in writing, signed by both of you, built on honest disclosure, and signed with time to spare. That is the whole foundation, and it is one any thoughtful couple can put in place together.

If the online path fits how you want to handle it, a South Dakota prenup can be completed with First for a flat $649 for the couple, with online notarization included. And if you would rather talk through your situation first, you can book a free 20-minute call to think it through, no commitment required.

Methodology

Attorney rate figures are drawn from the Clio 2025 Legal Trends Report for South Dakota and published Sioux Falls-area family-law rates, read in 2026. Couple totals combine those hourly rates across the hours a two-attorney prenup commonly takes, with each partner separately represented, so they are presented as a range rather than a single average. First's $649 flat fee is First's own published price for the couple.

Sources

First is not a law firm. The information and tools provided by First on this site are not legal advice and not a substitute for the advice of an attorney.