How a Proposition 19 Tax Base Transfer Works in California

When you use Proposition 19 to move your property tax base to a new home, one comparison decides your new tax bill: does your replacement home cost the same or less than your original home, or does it cost more? If it costs the same or less, your low tax base moves over with no change. If it costs more, you keep your low base and add only the extra amount you spent. Either way, you are taxed on far less than the full purchase price of the new home.

Key Facts

• One comparison drives the whole transfer: the market value of the home you sold versus the market value of the home you bought.

• The value you carry is your factored base year value — the low taxable value you built up under Proposition 13, often well below what your home is worth today.

• If the replacement home costs the same or less, your low base transfers with no adjustment.

• If the replacement home costs more, your new taxable value equals your old base plus the difference in market value between the two homes.

• A timing cushion can work in your favor: buying within one year after selling gives your old home's value a 5 percent bump for the comparison; buying within the second year gives it a 10 percent bump. That smaller difference lowers the amount added to your base.

• A one-time supplemental tax bill usually follows the transfer to reconcile the account.

What Does a Prop 19 Tax Base Transfer Actually Do?

It lets you keep the low property tax base you built up under Proposition 13 instead of losing it the moment you sell. When you sell a home, the county normally resets the taxable value to the sale price for the new owner. Under Proposition 19, a qualifying seller gets an exception. Their factored base year value — not the sale price — becomes the starting point for the new home's tax assessment.

The factored base year value is what California assessors call the taxable value a long-time owner carries. It started at their purchase price and has grown by no more than 2 percent per year under Prop 13. For someone who bought decades ago, it is usually a small fraction of today's market value, and it represents real savings: often thousands of dollars per year.

What Happens When the New Home Costs the Same or Less?

This is the cleanest outcome. If your replacement home's market value is equal to or less than your original home's market value, your factored base year value transfers with no change at all.

Downsizing does not lower your base further. If you move from a $700,000 home with a $200,000 factored base year value to a $500,000 home, your taxable value in the new home is still $200,000 — not some smaller number. You keep the savings you already have; you do not multiply them. For most people moving to a similar or smaller home, the entire story ends there: the low base moves, and the new tax bill looks like the old one.

What Happens When the New Home Costs More?

Proposition 19 does not cut you off if you buy up. It gives partial relief. You keep your low base and add only the amount by which the new home costs more than the old one.

The formula in plain terms: your new taxable value equals your factored base year value plus the difference in market value between the two homes.

Here is a concrete example. Say your original home has a factored base year value of $100,000 and you sell it for $400,000. You buy a replacement home for $600,000. The difference in market value is $200,000. Your new taxable value is $100,000 plus $200,000, which is $300,000. Instead of being taxed on the full $600,000 purchase price, you pay tax on $300,000 — roughly $3,000 per year at the basic 1 percent rate instead of roughly $6,000. That is a real and lasting saving, year after year.

What Is the Timing Cushion — and How Does It Help?

The law does not always compare your new home's price to your old home's price at face value. When you buy after you sell, it gives your old home's value a small boost before making the comparison. A higher comparison value means a smaller difference gets added to your base.

The schedule works like this. If you buy your replacement before you sell your original home, there is no cushion — the comparison is straight across at 100 percent of the sale price. If you buy within the first year after selling, your old home's sale price is treated as 5 percent higher for the comparison. If you buy within the second year after selling, it is treated as 10 percent higher.

Using the same example: if you sell for $400,000 and buy within the first year, the comparison uses $420,000 (5 percent more) instead of $400,000. The difference between $600,000 and $420,000 is $180,000, not $200,000. Your new taxable value becomes $100,000 plus $180,000, which is $280,000 instead of $300,000. The later you buy within the two-year window, the more the cushion works in your favor.

A Worked Example: Sacramento Homeowner Moving Up in Value

Here is how the math plays out from start to finish. A 67-year-old Sacramento homeowner has owned her home since 1994. Her factored base year value — her taxable value under Proposition 13 — is $155,000. Her home is now worth $650,000. She qualifies under the age-55-or-older group and wants to buy a larger home in El Dorado County to be closer to family.

She sells her Sacramento home for $650,000 and buys a replacement in El Dorado County for $800,000. She buys within the first year after selling, so the timing cushion applies. Her old home's value for the comparison is treated as $682,500 (5 percent more than $650,000). The difference between $800,000 and $682,500 is $117,500. Her new taxable value is $155,000 plus $117,500, which is $272,500.

Without the transfer, her El Dorado County tax bill would be based on the $800,000 purchase price — roughly $8,000 per year. With the transfer, it is calculated on $272,500 — roughly $2,725 per year. That is a saving of more than $5,200 every year going forward.

She files form BOE-19-B with the El Dorado County assessor. A few weeks later she receives a supplemental tax bill that reconciles the account for the period between closing and the assessor processing her claim. This is a normal, one-time adjustment — not a recurring charge.

Chapter 4 of Prop 19 Hero covers every variation of this calculation, including what happens when values are close, how to read a supplemental bill, and common errors people make when the timing cushion applies.

Summary

• One comparison decides your new taxable value: the market value of the home you sold versus the market value of the home you bought.

• If the replacement home costs the same or less, your factored base year value transfers with no adjustment.

• If the replacement home costs more, your new taxable value equals your old base plus the difference in market value.

• A timing cushion applies when you buy after selling: 5 percent if you buy within the first year, 10 percent within the second year, which reduces the amount added to your base.

• A one-time supplemental tax bill usually follows the transfer to true up the account.

• Running the math before you move — base plus any difference — shows you exactly what to expect on your new tax bill.

Get the Full Picture

Read the book. Prop 19 Hero walks through every variation of the transfer calculation, covers the timing cushion in full, and explains what to do when the supplemental bill arrives. Find it on Amazon.

Talk to Bart. If you own a home in Sacramento and want to run the numbers before you list, Bart Hubbard can show you exactly what your tax bill will look like in your next home. Reach out at Prop19Hero.com.

About the Author

Bart Hubbard is a California real estate associate at HomeSmart ICARE Realty (DRE #01815497) and a C.A.R. Certified Probate & Trust Specialist. He wrote Prop 19 Hero to give California homeowners 55 and older a clear, practical guide to the property tax rules that affect every move they make. He works with buyers and sellers throughout the Sacramento area. Reach him at [email protected] or www.prop19hero.com.