The Two Locks Holding San Diego Inventory in Place: Rate Lock and Prop 13

If you have spent any time trying to buy a home in San Diego over the last few years, you have probably heard the same explanation a dozen times. Inventory is low because rates went up. Sellers do not want to give up their cheap mortgages.

That is partially right, but it is missing half the picture. There are two distinct supply locks operating on California housing right now, and they compound each other in ways that make this inventory shortage durable in a way most national real estate commentators do not appreciate. As someone who reads bond market data for a living and represents 92130 buyers and sellers on the side, I see this question from both ends most days, and the standard explanation almost always understates what is actually keeping inventory tight.

The first lock is mortgage rate lock, which gets most of the attention. The second is California's property tax base lock from Proposition 13, which most outside observers either ignore or misunderstand. Both are real, both are large, and both apply to the same homeowner at the same time. That stacking is what makes California's situation different from the rest of the country.

Let's break down exactly how these two locks function, starting with the one that is more familiar to most readers.

The First Lock: Mortgage Rate Lock

The mortgage rate lock effect is straightforward to understand. A homeowner who locked in a 3 percent mortgage in 2020 or 2021 has a financial asset on their hands. Selling that home means giving up the low rate. Rebuying at today's rates means starting over at roughly 6.2 percent on a new loan.

According to the California Legislative Analyst's Office Housing Affordability Tracker (Q4 2025, published January 2026), 77 percent of California homeowners with mortgages currently hold rates below 5 percent. The average rate before 2022 was around 3 percent. Current 30-year rates sit around 6.2 to 6.4 percent. The gap between what existing homeowners pay and what new buyers face has not been this wide in modern memory.

The math on a typical California home illustrates how large this gap is in dollar terms.

That is roughly $33,600 per year in additional payment cost, or close to $1 million in additional interest over the life of a 30-year loan, just to swap one home for another similar one. Even on more typical California home prices, the LAO estimates the cost to be around $180,000 over the life of the loan, an 11 percent increase in monthly payments compared to staying put.

This is not a small number. For most homeowners, it is enough to make moving financially irrational unless something else in life forces the decision. Job relocation, divorce, downsizing in retirement, or a death in the family are the common reasons people sell despite the rate lock. Lifestyle changes that used to drive moves, like wanting more space or a different neighborhood, mostly do not clear that bar.

The lock is starting to fade as time passes. Each year, more homeowners refinance into higher rates, sell despite the cost, or pass the home through inheritance to a generation with a different cost basis. By early 2026, the share of mortgage holders below 3 percent is roughly equal to the share above 6 percent. But the absolute majority of California homeowners are still locked in, and the math still favors staying put for most of them.

The Second Lock: Prop 13 Property Tax Base

The second lock is California-specific and gets much less attention than rate lock, even though it can be just as financially significant for the homeowner.

California Proposition 13, passed in 1978, established the modern framework for property tax in the state. The mechanics are straightforward. Your property tax base is set at the price you paid when you purchased the home. From that point forward, the assessed value can increase by no more than 2 percent per year for as long as you remain the owner, regardless of how much the market value of the home has actually risen.

For a homeowner who purchased decades ago, this creates a property tax bill that is locked in at a fraction of what a comparable new buyer would pay. The longer you have owned, the larger that gap is.

Consider a homeowner who purchased a Carmel Valley home for $450,000 in 1998. Under Prop 13, their assessed value can grow by no more than 2 percent annually. After 28 years of compounding at the maximum allowed rate, the assessed value would be roughly $785,000, even if the home's actual market value today is $2.8 million.

That homeowner is paying about $8,600 per year in property tax. If they sell and buy a similar home, their new property tax base resets to whatever they pay for the new home. On a $2.8 million purchase, the property tax bill would be closer to $30,800 per year. Even if they downsize to a smaller home worth $1.8 million, their property tax would still roughly double.

This is a separate cost from the mortgage rate differential. It applies even if the homeowner is buying with all cash and has no mortgage at all. And unlike the rate lock, which slowly fades as rates normalize, the Prop 13 lock compounds in the homeowner's favor for as long as they stay in the home.

Why California Is Different

Most of the national commentary on the housing inventory shortage focuses on rate lock alone. That makes sense in most states, where rate lock is the dominant force.

California is the most prominent state where both locks operate at full strength, and they compound each other. A long-term California homeowner deciding whether to sell does not just face the question of whether their new mortgage payment would be higher. They face the question of whether their new mortgage payment plus their new property tax bill would be higher, often by tens of thousands of dollars per year combined.

The behavioral response is exactly what economic theory would predict. California has one of the lowest residential turnover rates in the country. Homeowners stay in place longer than they would in states without Prop 13. New construction has not kept pace with population growth, partly because of land use constraints and partly because building permits have not recovered to historical norms. The result is a state with persistently low inventory, persistently high prices, and persistently constrained mobility.

This dynamic is especially visible in coastal markets like San Diego, where home prices have appreciated dramatically over the past two decades. The longer a homeowner has been in their home, the larger both locks become. The gap between what they pay today and what they would pay if they sold and rebought is wide enough to make moving financially irrational for most of them, even with significant equity in the home.

I see this play out at the kitchen table in Carmel Valley regularly. A homeowner who bought their home for $700,000 in 2005 has watched the market value climb past $2.5 million. On paper, they are sitting on enormous equity. In practice, they cannot move within California without nearly tripling their property tax bill and adding thousands per month in new mortgage payments. The conversation usually shifts from "should we sell" to "how do we structure our lives to stay." That is the lock working as designed.

The Partial Release Valve: Prop 19

There is one important exception to the property tax lock, and it is a recent one.

California Proposition 19, passed in November 2020 and effective April 1, 2021, allows homeowners aged 55 or older, severely disabled persons, and those whose homes have been damaged or destroyed by natural disaster to transfer their existing property tax base to a new primary residence anywhere in California. The transfer can be used up to three times in a lifetime for those over 55, and it works even if the new home is more expensive than the old one (with a small adjustment for the price difference).

For a long-term homeowner who is approaching retirement and considering a downsize, Prop 19 effectively removes the property tax penalty that has historically locked them in place. The mortgage rate question still applies, but Prop 19 eliminates the second compounding force.

This matters more than most people realize. The largest pool of locked supply in California is owned by long-term homeowners now in their 60s, 70s, and 80s, many of whom have been holding their homes for 20 to 40 years. Their kids are grown and out of the house. Their original homes are larger than they need. Many of them would prefer a smaller home in a different location. Before Prop 19, the property tax math made that move prohibitively expensive. After Prop 19, it does not.

I am starting to see early signs of this generation finally listing. It is not a flood, but it is a measurable shift compared to where things were three or four years ago. Over the next decade, Prop 19 transfers may turn out to be one of the more meaningful supply unlock mechanisms in California real estate.

What This Means for Buyers and Sellers

If you are trying to make sense of the San Diego market, the two locks frame is one of the more useful tools you can carry around.

For buyers, the locks explain why prices have not corrected the way many predicted they would when rates rose. A typical economic textbook would suggest that higher rates should crater home prices because affordability collapses. That has not happened in California because the supply side of the equation is locked in place. Prices have softened modestly in some segments, but the structural support from constrained supply is real and durable.

The strategic implication for buyers is that waiting for a major price correction may not pay off the way it would have in past cycles. Some softening in specific segments and price points is realistic. A 15 to 20 percent drop across the board is not, unless something forces simultaneous breaks in both supply locks. That would require either a sustained drop in mortgage rates back below 5 percent or a structural change to Prop 13. Neither is in the immediate forecast.

For sellers, the locks explain why your decision is almost always more nuanced than just looking at your home's current market value. The right question is not just "what is my home worth," it is "what would my total cost of housing be if I sold and bought a similar home today, including the new mortgage rate, the new property tax base, and transaction costs." For most long-term homeowners, that comparison reveals that staying put is significantly cheaper than moving, even after accounting for the equity unlock.

The exception is homeowners who qualify for Prop 19. For them, the property tax lock is removable, and the only remaining question is the mortgage rate differential. That can still be substantial, but it is half of what a younger homeowner would face on the same transaction.

Common Questions About California Supply Lock

What is the mortgage rate lock effect?

The mortgage rate lock effect is the phenomenon where homeowners with low rate mortgages are reluctant to sell because doing so would force them to take on a new mortgage at a much higher rate. According to the California Legislative Analyst's Office, roughly 77 percent of California homeowners currently hold mortgages below 5 percent, while new borrowers face rates around 6.2 percent. Selling and rebuying at current rates can add about 11 percent to monthly payments and roughly $180,000 over the life of a 30-year loan for a typical California homeowner.

How does Proposition 13 lock California housing supply?

California Proposition 13, passed in 1978, limits annual property tax increases to 2 percent for as long as the homeowner stays in the home. Selling and buying a new home at today's market value resets the tax base to that purchase price, which can mean a tax bill that is several times higher. For long-term homeowners, this property tax differential creates a strong financial incentive to stay in the current home rather than move, even if their housing needs have changed.

What is California Proposition 19?

California Proposition 19, passed in November 2020 and effective April 1, 2021, allows homeowners aged 55 or older, severely disabled, or affected by a natural disaster to transfer their existing property tax base to a new primary residence anywhere in California, up to three times in their lifetime. For longtime owners considering a downsize, Prop 19 partially unlocks the property tax constraint that has historically kept them from selling.

When will San Diego inventory unlock?

The mortgage rate lock effect is gradually fading as time passes. Each year, more homeowners refinance at higher rates, sell despite the cost, or pass the home through inheritance. By early 2026, the share of mortgage holders below 3 percent is roughly equal to the share above 6 percent, and inventory across California has begun to rise. The property tax lock is more durable, but Proposition 19 has opened a partial release valve for homeowners over 55. Full normalization is years away, but the early stages are visible now.