How Proposition 13 works, and what it does to your property tax bill
California assesses property tax on what you paid, not what your home is worth today. That single rule explains most of what is strange about the state's housing market.
Almost every peculiarity of California real estate traces back to one 1978 ballot measure. Proposition 13 changed the question the county assessor asks. Instead of "what is this property worth today", the assessor asks "what did the owner pay for it, and how long ago".
That distinction produces effects that surprise people arriving from other states, and it shapes decisions well beyond tax: when people sell, whether they renovate, how cities budget, and why a neighbour in an identical house can pay a fraction of what you pay.
The two rules that do the work
Proposition 13 does two things. It caps the base property tax rate at 1% of assessed value. And it limits how fast that assessed value can rise while you own the property — no more than 2% a year, regardless of what the market does.
Your actual bill is usually higher than 1%, because voters can approve additional levies on top: school bonds, local infrastructure measures, special districts. Those are added to the base rate, which is why effective rates differ from one county to the next and sometimes from one street to the next.
The 2% cap is the part that compounds. If the market rises 8% a year and your assessment rises 2%, the gap between what your home is worth and what you are taxed on widens every year you stay.
Reassessment: the moment the clock resets
The assessed value is reset to market value when the property changes ownership. That is the event Proposition 13 is built around, and it is why a long-held home and a recently sold one can sit side by side with wildly different bills.
New construction is treated similarly. Adding square footage triggers a reassessment of the new portion, though ordinary maintenance and repair do not. Replacing a roof is not an improvement in the assessor's sense; adding a second storey is.
Why this shapes the housing market
The lock-in effect is the most studied consequence. An owner who has held a property for twenty years carries a tax basis far below market. Selling means buying at today's prices and today's assessment, so the tax cost of moving can be large enough to keep people in homes they would otherwise leave.
That reduces turnover. Fewer listings from long-term owners means less supply in established neighbourhoods, which pushes buyers toward new construction on the edges of metropolitan areas — with the commuting and infrastructure costs that follow.
“The measure did not just cap a tax. It changed who moves, when, and where they move to.”
It also changes what cities do. Because property tax growth is capped and predictable, municipalities lean harder on sales tax and development fees. That is part of why California cities compete so intensely for retail and why fees on new housing are high — the revenue has to come from somewhere.
Commercial property
The same rules apply to commercial and industrial property, and the lock-in effect is stronger, because commercial buildings change hands less often and can be held indefinitely through entities. Reform proposals aimed at this — usually described as split-roll — have appeared on the ballot repeatedly and have not passed.
What to check on your own bill
- Your assessed value, which appears on the county assessor's notice and is not the same as any market estimate you have seen online.
- The base 1% and the voter-approved additions listed separately beneath it.
- Whether any exclusion you claimed is reflected, particularly after a transfer.
- Whether a recent permit triggered a partial reassessment you were not expecting.
If the assessed value looks wrong, county assessors have a formal appeal process with a filing window. Missing that window generally means waiting a year.
