Free tool · California
The Moore/Marsden calculator.
One spouse bought the house before the marriage; the mortgage got paid during it. The community owns a slice. Every California family lawyer has to run this number, most still do it by hand, and the fights it starts are often worth less than the hour spent fighting. Enter the numbers and get the interest, with the math shown line by line.
The rule, in two paragraphs
When community money reduces the principal on one spouse's separate-property home, the community buys in: a pro tanto interest equal to the ratio of community principal payments to the original purchase price (In re Marriage of Moore (1980) 28 Cal.3d 366). Only principal counts — interest, taxes, and insurance buy nothing. Appreciation before the marriage belongs entirely to the owner spouse; the community shares only the appreciation during the marriage, in proportion to its percentage (In re Marriage of Marsden (1982) 130 Cal.App.3d 426), measured to the date of trial (In re Marriage of Sherman (2005) 133 Cal.App.4th 795).
The number is almost always smaller than either side expects. The community percentage divides principal paid by a purchase price often set decades ago, so a house with modest principal reduction throws off a community share in the low single digits — and each spouse takes only half of that. Before spending a billed hour arguing over the appreciation figure, run both versions here and look at the delta. It is frequently smaller than the cost of the argument.
What a refinance does
Refinancing during the marriage moves this number more than anything else on the page. A loan taken during marriage is presumptively a community loan (Gudelj v. Gudelj (1953) 41 Cal.2d 202; In re Marriage of Grinius (1985) 166 Cal.App.3d 1179 — the presumption falls only where the lender relied solely on separate property). If the refinance loan is community, the entire balance it paid off counts as a community contribution to the purchase price (In re Marriage of Branco (1996) 47 Cal.App.4th 1621) — a house that was 95% separate can become majority community in one signing. Cash pulled out above the payoff buys no additional interest in the house (In re Marriage of Nelson (2006) 139 Cal.App.4th 1546). In practice, many judges resist the Branco result and find the refinance loan separate on modest evidence. The calculator runs both characterizations so you can see the two numbers before anyone stakes out a position.
The calculator
Dollar amounts; commas welcome. The math updates as you type.
The math, shown
- Improvements. Community-funded improvements to separate property raise a related but distinct analysis (Bono v. Clark (2002) 103 Cal.App.4th 1409, as corrected by Sherman); they are not principal and are not modeled here.
- Retitled property. If the house was deeded into both names during the marriage, the question becomes a Family Code § 2640 reimbursement, not Moore/Marsden — a different statute with a different result. DivySplit's real-property worksheet routes between the two from plain-fact questions.
- Tracing disputes. The calculator takes "community principal" as an input; proving which dollars were community is the actual fight in many cases.
- Alternate valuation dates. Trial-date value is the default (Fam. Code § 2552(a); Sherman); a court can set an earlier date on a proper showing under § 2552(b).
- Epstein credits and Watts charges — post-separation payment and use questions live outside this formula.