Moore-Marsden Calculation
When one spouse owned a home before marriage and the couple used marital income to pay down the mortgage, California law gives the community a share of the home's equity. Here's exactly how the math works.
What is the Moore-Marsden rule?
The Moore-Marsden rule (named after the California cases In re Marriage of Moore and In re Marriage of Marsden) establishes that when community funds — income earned during marriage — are used to pay down the mortgage on one spouse's separate-property home, the community earns a proportional interest in that home.
The key insight: even if the non-titled spouse is never on the deed, they can have a legitimate financial claim to a portion of the home's appreciation simply because marital income paid the mortgage. The formula calculates exactly how much.
Core principle
When does it apply?
What if a transmutation happened?
The Formula
Moore-Marsden formula
Community Ratio = Principal Paid During Marriage ÷ Original Purchase Price
Community Share of Appreciation = Community Ratio × Appreciation During Marriage
Total Community Interest = Principal Paid During Marriage + Community Share of Appreciation
The community ratio reflects how much of the original purchase price was paid off with community funds. That same ratio is then applied to the home's appreciation to determine the community's share of the gain.
Worked Example: Bob & Alice
Bob buys a home in 2015 — before he meets Alice. They marry in 2017 and separate in 2023. Throughout the marriage, their combined income pays down the mortgage. Does Alice have a claim to the home even though she's never been on the title?
| Item | Amount |
|---|---|
| Home purchase price (2015) | $500,000 |
| Bob's down payment | $100,000 |
| Original mortgage | $400,000 |
| Mortgage at marriage (2017) | $375,000 |
| Mortgage at divorce (2023) | $250,000 |
| Principal paid during marriage | $125,000 |
| Home value at marriage (2017) | $600,000 |
| Home value at divorce (2023) | $800,000 |
| Appreciation during marriage | $200,000 |
Property timeline
Step-by-Step Calculation
Community Principal Paydown
How much mortgage principal was paid using community (marital) income?
$375,000 − $250,000 = $125,000
Community Ratio
What fraction of the original purchase price did the community pay down?
$125,000 ÷ $500,000 = 25%
Community Share of Appreciation
The community's 25% ratio is applied to the home's appreciation during the marriage.
25% × $200,000 = $50,000
Total Community Interest
The community's total interest is the sum of principal paid down plus the share of appreciation.
$125,000 + $50,000 = $175,000
Final Equity Division
Total home equity is $550,000 ($800K value − $250K mortgage). The community pool of $175,000 is split 50/50. Bob keeps the remaining separate interest.
Alice (community 50%)
$87,500
15.9% of total equity
Bob (separate + community 50%)
$462,500
84.1% of total equity
Equity Breakdown
$550,000 total equity
Key Takeaways
Title doesn't determine everything
Community interest grows with every mortgage payment
Low appreciation = smaller community share
Consider adding a spouse to title carefully
Run these numbers for your property
Enter your home's purchase price, mortgage history, and key dates — the calculator applies the Moore-Marsden formula automatically and shows every step.
Open Calculator →Watch the video explainer
Plain-English walkthrough of how California divides property in a divorce.
Your Fair Half — the book
The complete guide to knowing what you're owed before you sign anything.
For informational purposes only. Not legal advice. Consult a licensed California family law attorney.