Prenuptial Agreement Requirements in South Dakota

At a glance

Requirements one by one

South Dakota uses the Uniform Premarital Agreement Act

S.D. Codified Laws § 25-2-25 gives §§ 25-2-16 through 25-2-25 the short title Uniform Premarital Agreement Act. Section 25-2-16 defines a premarital agreement as one between prospective spouses, made in contemplation of marriage, and intended to take effect upon marriage.

Under § 25-2-24, courts construe the act to make the law uniform among states that enacted it.

South Dakota did not enact the model act word for word. Most importantly, it left spousal-support contracting out of § 25-2-18, a deliberate omission the South Dakota Supreme Court addressed in Sanford v. Sanford.

The agreement needs both signatures and marriage activates it

Section 25-2-17 states the basic form directly: a premarital agreement “shall be in writing and signed by both parties.” It is enforceable without consideration. Under § 25-2-19, the signed agreement becomes effective upon marriage, not merely upon signing.

The act adds no notary, witness, or recording requirement

The statute titled “Formalities,” § 25-2-17, requires only the writing and both signatures. Sections 25-2-16 through 25-2-25 add no acknowledgment, notary, witness, attestation, or recording step for basic validity between the parties.

A notarized signature may help prove execution, but notarization is not one of the act's stated validity requirements.

Disclosure uses three alternatives within the unconscionability test

Under § 25-2-21(a)(2), inadequate disclosure defeats enforcement through a combined test. The agreement must have been unconscionable when signed, and the challenging party must establish all three listed conditions: no fair and reasonable disclosure, no voluntary express written waiver of further disclosure, and no actual or reasonably available adequate knowledge.

The waiver must be voluntary, express, and in writing. The statute does not say it must be a separate document.

Counsel and a pre-wedding interval are not statutory formalities

Sections 25-2-16 through 25-2-25 impose no independent-counsel mandate, written counsel advisement, fixed review period, or minimum number of days between signing and the wedding. That does not eliminate the separate requirement in § 25-2-21(a)(1) that execution be voluntary.

The statute supplies the enforcement test

The fairness source is statutory. Section 25-2-21 provides two routes to nonenforcement: involuntary execution, or execution-time unconscionability combined with all three disclosure failures. The court decides unconscionability as a matter of law.

The statute does not create a general enforcement-time second look based only on changed circumstances. Its unconscionability language points to when the agreement was executed.

Spousal-support waivers are void

In Sanford v. Sanford, 2005 SD 34, ¶ 38, the South Dakota Supreme Court held that a premarital provision purporting to limit or waive spousal support is void and unenforceable as contrary to public policy. The court tied that result to the Legislature's deliberate decision not to enact the model UPAA provision allowing modification or elimination of support.

Child support and custody remain outside private control

Section 25-2-18(b) says a prenup may not adversely affect a child's right to support. Section 25-4-45 keeps custody with the divorce court and directs it to the child's best interests. Other personal-rights terms are allowed under § 25-2-18(a)(7) only if they do not violate public policy or a statute imposing a criminal penalty.

Changes after marriage require another signed writing

Under § 25-2-20, amendment or revocation after marriage is possible only through a written agreement signed by both parties. The amendment or revocation is enforceable without consideration. The statute does not add notarization to this change mechanism.

What trips people up

• A bad support clause does not necessarily destroy every property term. Sanford held that a void support waiver may be severed from valid portions without invalidating the entire agreement.
• A notary does not replace financial disclosure. In Goeden v. Goeden, 2024 S.D. 51, one party signed a notarized agreement nine days before the wedding, but the court still affirmed nonenforcement because undisclosed retirement, health-savings, and bank assets left the statutory unconscionability-and-disclosure test unsatisfied.
• Marriage pauses a limitations period, but equitable delay defenses remain. Under § 25-2-23, an applicable statute of limitations is tolled during the marriage while preserving defenses such as laches and estoppel.

Common questions

Must the disclosure give exact values?

Not necessarily. Sanford, 2005 SD 34, ¶ 44, says a list of assets and liabilities with approximate values may suffice if it gives the other spouse a reasonable approximation of the magnitude of net worth.

Can the agreement address death and estate-planning arrangements?

Yes. Section 25-2-18(a) permits terms about property disposition at death, wills or trusts used to carry out the agreement, and ownership or disposition of a life-insurance death benefit.

What if the marriage is later determined to be void?

Section 25-2-22 limits an agreement that otherwise would have been a premarital agreement to enforcement necessary to avoid an inequitable result.

Statutes and sources

• S.D. Codified Laws §§ 25-2-16, 25-2-24, and 25-2-25 — definition, uniform construction, and short title. Official South Dakota Legislature (accessed 2026-07-28).
• S.D. Codified Laws §§ 25-2-17 and 25-2-19 — writing, signatures, no consideration, and effectiveness upon marriage. Official § 25-2-17; official § 25-2-19 (accessed 2026-07-28).
• S.D. Codified Laws § 25-2-18 — permitted subjects, public-policy limit, and child-support protection. Official South Dakota Legislature (accessed 2026-07-28).
• S.D. Codified Laws § 25-2-21 — voluntariness, unconscionability, disclosure, written waiver, adequate knowledge, and court decision. Official South Dakota Legislature (accessed 2026-07-28).
• S.D. Codified Laws § 25-2-20 — amendment and revocation. Official South Dakota Legislature (accessed 2026-07-28).
• S.D. Codified Laws §§ 25-2-22 and 25-2-23 — void marriages, limitations tolling, and equitable defenses. Official § 25-2-22; official § 25-2-23 (accessed 2026-07-28).
• S.D. Codified Laws § 25-4-45 — court-controlled custody and child best interests. Official South Dakota Legislature (accessed 2026-07-28).
• Sanford v. Sanford, 2005 SD 34, 694 N.W.2d 283 — support-waiver bar, severability, and disclosure precision. Opinion text (accessed 2026-07-28).
• Goeden v. Goeden, 2024 S.D. 51 — current application of the disclosure and unconscionability test. Official South Dakota Unified Judicial System opinion (accessed 2026-07-28).