Prenuptial Agreement Asset Division Calculator

Key Concepts: Separate vs. Marital Property

Separate property at marriage

Separate property generally refers to assets and debts that belong to one spouse individually, such as what they owned before the marriage. In this calculator, you can enter:

• Spouse A separate assets ($): value of A’s assets when the marriage begins (for example, savings, investments, real estate).
• Spouse B separate assets ($): value of B’s assets at the same point in time.

The tool treats these as remaining with the original owner in both the no‑prenup and prenup scenarios, unless you choose to reflect marital contributions in a different way through your inputs or under a custom agreement.

Marital or community property

Marital property (sometimes called community property) is a broad label often used for assets and debts accumulated during a marriage, such as wages, joint savings, or loans taken out together. The calculator asks for:

• Marital assets ($): the total value of assets earned or acquired during the marriage that you want to model.
• Marital debts ($): the total balance of debts taken on during the marriage that you want to include.

The calculator combines these into net marital property:

You can then choose how to split this net marital property between the spouses in the no‑prenup and prenup scenarios.

Modeling Marital Contributions to Separate Property

Over time, money earned during the marriage is often used to improve or pay down property one spouse owned before the marriage. Some legal systems may treat part of this increase in value as marital or joint. To give you a way to reflect this concept at a high level, the calculator includes optional fields for marital contributions to separate assets:

• Marital contributions to A’s separate assets ($): payments made during the marriage that reduced debts or increased the value of property that originally belonged only to Spouse A.
• Marital contributions to B’s separate assets ($): the same idea, but for Spouse B.

Example: Spouse A owns a condo before marriage. During the marriage, both spouses use marital income to pay down the mortgage by $40,000. You could enter 40000 as the marital contribution to A’s separate assets to highlight that a meaningful portion of marital resources went into that property, even though the condo itself is still treated here as A’s separate asset.

This calculator does not decide how courts would treat these contributions. Instead, it gives you a transparent way to record and compare them under your own assumptions or under a proposed prenup.

No‑Prenup vs. Prenup Splits

No‑prenup marital split

The No‑prenup marital split to Spouse A (%) field is your estimate of how net marital property might be divided if there were no prenuptial agreement in place. For example:

• Use 50 if you want to model an even 50/50 share.
• Use another percentage (for example, 60 to A / 40 to B) if you expect an unequal division.

This is not a forecast of what any particular judge or jurisdiction would do. It’s simply a scenario that you define for comparison purposes.

Prenup marital split

The Prenup marital split to Spouse A (%) field represents how you might agree to share net marital property in a prenuptial agreement. You can explore different options, such as keeping it 50/50 or setting a different split to reflect circumstances like uneven income or business risk.

In both cases, the calculator uses the percentage for Spouse A and assigns the remainder (100 minus that percentage) to Spouse B. So if you enter 55 for Spouse A, Spouse B is modeled at 45.

Interpreting the Results

Once you enter your values and run the calculator, you will typically see a side‑by‑side comparison of how much each spouse receives under the no‑prenup scenario and under the prenup scenario. While the exact layout may vary, you can think of the outputs in terms of three main components:

• Separate property kept by each spouse (A’s premarital assets; B’s premarital assets).
• Share of net marital property allocated to each spouse, based on the percentages you entered.
• Effect of marital contributions to separate assets, which may be shown as additional context rather than as a separate legal category.

Instead of focusing only on totals, you can also compare the balance between spouses. For instance, you might look at whether a proposed prenup increases or decreases the gap between what Spouse A and Spouse B would receive under your assumptions.

Worked Example (Illustrative Only)

Imagine the following simplified situation:

• Spouse A separate assets: $150,000
• Spouse B separate assets: $20,000
• Marital assets: $200,000
• Marital debts: $50,000
• No‑prenup marital split to Spouse A: 50%
• Prenup marital split to Spouse A: 60%
• Marital contributions to A’s separate assets: $30,000
• Marital contributions to B’s separate assets: $0

Net marital property is $150,000 ($200,000 − $50,000). Under your inputs:

• No‑prenup scenario: each spouse receives $75,000 of net marital property.
• Prenup scenario: A receives 60% ($90,000) and B receives 40% ($60,000).

Total amounts modeled by the calculator might look like this:

• Spouse A (no‑prenup): $150,000 separate + $75,000 marital = $225,000.
• Spouse A (prenup): $150,000 separate + $90,000 marital = $240,000.
• Spouse B (no‑prenup): $20,000 separate + $75,000 marital = $95,000.
• Spouse B (prenup): $20,000 separate + $60,000 marital = $80,000.

The $30,000 in marital contributions to A’s separate assets appears in the context section of the results to remind you that marital resources helped build A’s property. The tool does not reclassify those dollars on its own—it simply makes the contribution visible so you can consider how you might want to treat it in a prenup or discussion with an attorney.

Practical Use Cases

Premarital home owned by one spouse

One spouse owns a house before marriage, and both spouses expect to use marital income to pay the mortgage and improve the property. They can use the calculator to:

• Enter the home’s equity as that spouse’s separate property.
• Estimate future marital assets and debts.
• Record estimated marital contributions to the home over time.
• Compare a 50/50 no‑prenup assumption with a custom prenup split designed to reflect their preferences.

Unequal expected earnings or business risk

Another couple expects one spouse to build a higher‑risk business while the other has a more stable income. They can:

• Enter current separate savings and investments for each spouse.
• Model potential future marital assets and debts related to the business.
• Test different marital property splits (for example, 50/50 vs. 60/40) to see how each approach changes the total amounts each spouse might receive.

Assumptions and Limitations

This calculator is deliberately simplified. It makes several important assumptions and has limitations you should keep in mind:

• Generalized model only: The tool does not reflect the specific laws of any country, state, or region. Actual outcomes depend on local statutes and court decisions.
• Limited asset types: It does not separately model retirement accounts, stock options, business interests, taxes, or transaction costs. You may need professional help to account for these items.
• No predictions of court behavior: The "no‑prenup" split is whatever you choose to enter. Courts may divide property differently based on many factors not captured here.
• Simplified treatment of contributions: Marital contributions to separate assets are displayed for transparency but are not automatically converted into ownership shares or legal rights.
• Estimates, not guarantees: All values are user‑supplied estimates. Small changes in inputs can lead to different results, and real‑world events (market changes, new debts, inheritances) are not modeled.
• Not legal, tax, or financial advice: The calculator is an educational planning tool only. For any actual prenuptial agreement or legal decision, you should consult a qualified attorney and, where appropriate, tax and financial professionals.

Using this tool alongside professional advice can help you ask clearer questions and better understand the trade‑offs you are considering, but it cannot replace personalized guidance.

Why People Consider Prenups

Prenuptial agreements are often misunderstood. In popular culture they can sound like a cynical bet against love. In real life, they are usually a pragmatic financial tool. A prenup is simply a contract that defines what happens to property and debt if a marriage ends by divorce or death. Couples consider them for many reasons: one partner owns a business, expects an inheritance, has children from a prior relationship, or is bringing substantially more assets into the marriage. Some couples use a prenup to avoid uncertainty; others use it to protect both partners from the financial chaos that a contested divorce can create.

Even if you never expect to use a prenup, thinking about how property division works is healthy. Every state has a default system for dividing property. If you do nothing, those default rules apply. A prenup lets you replace parts of those rules with terms you both agree to up front, when communication is calm and cooperative. This calculator helps you see the difference between those two paths in a simple, transparent way.

Community Property vs. Equitable Distribution

U.S. states generally follow one of two approaches:

• Community property states (such as California, Texas, and Arizona) treat most assets acquired during marriage as jointly owned 50/50. Separate property owned before marriage or received as a gift/inheritance typically stays separate, unless commingled.
• Equitable distribution states divide marital property in a way a court deems fair, which may be close to 50/50 but can differ based on income, caregiving, duration of marriage, and contributions.

This estimator uses a neutral baseline: it assumes marital property is split 50/50, and separate property stays with its original owner. That mirrors many outcomes and provides a consistent comparison to a prenup. If you live in an equitable distribution state and expect a different split, you can approximate it by adjusting the “no‑prenup marital split” field.

Key Terms Used Here

• Separate property. Assets owned by a spouse before marriage, or received individually as gifts or inheritances.
• Marital (community) property. Assets acquired or grown during marriage from joint effort.
• Commingling. Mixing separate and marital property in a way that can convert part of a separate asset into marital property (for example, using marital income to pay down a premarital mortgage).
• Marital contribution to separate property. Payments or investments made during marriage that increase the value of a separate asset.

The Simple Division Model

Let each spouse have separate property at marriage (SA and SB). During marriage, the couple accumulates marital assets (M) and marital debts (D). If marital property is split by a marital split percentage p to spouse A and (1−p) to spouse B, then the no‑prenup outcome is:

A prenup can change three things in a simple planning model: (1) the marital split percentage, (2) whether certain separate assets become partially marital due to commingling, and (3) whether one spouse receives a fixed “lump sum” or reimbursement for specific contributions. This calculator focuses on the first two because they are common and easy to model.

Worked Example

Suppose Alex and Jordan are marrying. Alex has $220,000 of separate assets (mostly retirement savings and a condo). Jordan has $60,000 of separate assets. Over 8 years, they accumulate $380,000 of marital assets and $40,000 of marital debt. They live in a community property state, so a baseline marital split is 50/50. They also use marital income to pay $50,000 toward Alex’s premarital condo mortgage, which they agree should be treated as a marital contribution that creates marital equity.

No prenup baseline. Net marital property is $380,000 − $40,000 = $340,000. Each spouse receives 50% = $170,000 of that. Alex receives $220,000 + $170,000 = $390,000. Jordan receives $60,000 + $170,000 = $230,000.

Prenup scenario. They agree that marital property will be split 60/40 in favor of Jordan to recognize caregiving and career sacrifice, and that the $50,000 mortgage paydown creates marital equity split on the same 60/40 basis. Net marital property is still $340,000. Jordan gets 60% = $204,000; Alex gets 40% = $136,000. Alex’s separate property remains $220,000. Alex total = $356,000. Jordan total = $264,000. The prenup narrows the gap and reflects their shared intent.

The specific numbers depend on the marriage’s reality, but the exercise shows why a prenup is a tool for aligning outcomes with values, not just protecting wealth.

Comparison Table: Common Prenup Structures

Limitations and Assumptions

This calculator uses a simplified model so it is useful to a broad audience. It assumes:

• All separate property values are clearly identified and remain separate unless you enter marital contributions.
• Marital assets and debts are pooled and split by a single percentage.
• Appreciation, tax basis, and liquidity are ignored; values are in today’s dollars.
• Support obligations (alimony/child support) are not modeled. Many prenups can limit alimony but not child support.

Real divorces involve tracing, valuation disputes, business goodwill, and state‑specific rules. Use this tool to understand levers and talk productively, then consult a family‑law attorney to draft or review any agreement.