A $4,000 Prenup to Protect a $200,000 Business? The Expected-Value Math
$200K of premarital business equity, split 50/50 without a prenup, times a 41% divorce probability — that's $41,000 of expected risk against a $4,000 attorney bill. Run your own numbers instead of guessing whether it's worth the awkward conversation.
An expected-value question, not a certain one
We ran a common scenario through the calculator: $200,000 of premarital business equity, a state where roughly half of that would likely be treated as divisible without a prenup, and the CDC/NCHS estimate that about 41% of first marriages end in divorce. That works out to $41,000 of expected risk — against a $4,000 attorney bill for drafting the agreement (both parties typically need separate counsel). The prenup doesn't guarantee anything; it changes the expected value of a decision neither partner controls the outcome of.
The math flips fast at the other end: someone with $15,000 in premarital savings and the same $4,000 attorney cost has an expected benefit of about $3,075 — less than the cost of the agreement itself. The calculator exists because "should we get a prenup" gets asked in absolutes when it's actually a threshold question tied to how much premarital wealth is actually at stake.
How the math works
Expected assets at risk = premarital assets × split share without a prenup × divorce probability. Net expected benefit = expected assets at risk − attorney cost. Breakeven asset value = attorney cost ÷ (split share × divorce probability) — the premarital asset value at which the prenup exactly pays for itself in expectation.
The default 41% divorce probability comes from CDC/NCHS 2024 data on first marriages — notably below the commonly cited but outdated "50%" figure. The split-share-without-a-prenup input is yours to set because it genuinely varies by state (community property states split marital appreciation differently than equitable-distribution states) and by whether the assets stayed cleanly separate or got commingled with joint funds over the marriage.
Math runs locally. Inputs never leave your browser.Source on github.
Where this calculation doesn't apply
- Little or no premarital wealth to protect.If both partners are starting from a similar, modest financial position, the expected benefit is small relative to the attorney cost regardless of the divorce probability assumed.
- The real motivation is non-financial.Some couples want a prenup for clarity and reduced future conflict, not asset protection — that value isn't captured by this expected-value framing at all.
- A strict separate-property state already protects premarital assets well.If your split-share-without-a-prenup estimate is genuinely low, a prenup adds less financial value — though it can still clarify commingling risk over a long marriage.
- Assets are illiquid or hard to value (a business, real estate).A prenup with a clear valuation methodology for these assets is often worth more than this dollar-figure framing suggests, since ambiguity itself is costly in a dispute.
What to actually do
- List out premarital assets honestly — a business, an inheritance, home equity — before estimating what a prenup would protect.
- Get a real attorney-fee quote for your state; costs vary by complexity and whether both parties retain separate counsel (required for enforceability in most states).
- Have the conversation early — state laws generally require prenups to be signed with enough time before the wedding to avoid a duress challenge.
- Consider a postnuptial agreement if the window before the wedding has already closed; the same asset-protection logic applies, drafted after marriage instead.
- Talk to a family-law attorney about your specific state's rules on execution requirements and what assets your split-share estimate should realistically reflect.