How Prop 19 Portability Works for Sonoma Moves

If property taxes are the one thing keeping you from making your move to Sonoma, you are not alone. Many owners want to right-size or relocate but worry that buying at today’s prices will spike their annual tax bill. Proposition 19 portability can change that math and make the move work. In this guide, you’ll learn what Prop 19 portability is, who qualifies, how the transfer calculation works, the Sonoma County filing steps, and common situations to watch. Let’s dive in.

What Prop 19 portability means for Sonoma

Prop 19 lets certain homeowners transfer the taxable value of their current primary residence to a replacement primary residence anywhere in California. That means you can move to or within Sonoma County and keep a lower assessed value than you would get if the county reassessed you at full market value.

You may qualify if you meet at least one of these conditions:

• You are age 55 or older.
• You are severely and permanently disabled.
• Your prior home was made uninhabitable by a wildfire or other qualifying disaster.

Portability applies to primary residences only. Your original home must have been your principal residence at the time of the transfer or triggering event, and your replacement home must be intended as your primary residence. Intercounty transfers are allowed, so moves between San Francisco and Sonoma are eligible.

Who qualifies and when to file

Eligibility hinges on two things: your status and how you use the properties. You must be 55 or older, severely and permanently disabled, or a disaster victim whose prior home was rendered uninhabitable. Both the original and replacement properties must be your principal residences.

There is a filing window for your claim. Homeowners generally file with the assessor in the county where the replacement property is located within a specified period after purchase or completion of new construction. Many counties cite a window of up to three years, but you should confirm current Sonoma County deadlines before you close.

Filing early helps. Submitting your claim during escrow or immediately after closing gives the assessor time to process the transfer and reduces the chance of surprise supplemental tax bills later.

How the tax base transfer works

When your claim is approved, Sonoma County transfers the assessed value from your original principal residence to your new home, then adjusts it for any difference in market values at the time of transfer. This approach preserves your Prop 13 protection and helps keep your ongoing taxes lower than a full reassessment to current market value.

Conceptually, the calculation works like this:

• New assessed value = Original assessed value + (Market value of replacement home − Market value of original home).
• If your replacement home’s market value is higher than your original home’s value, the difference is added to your original assessed value.
• If your replacement home’s market value is lower, your new assessed value is reduced accordingly.

County assessors determine market values using sales data or appraisals and apply statutory rules. The assessed value cannot exceed market value.

Example: Buying a more expensive home

• Original home: assessed value $200,000, current market value $400,000.
• Replacement home: market value $600,000.
• Calculation: $200,000 + ($600,000 − $400,000) = $400,000 assessed value on the replacement home.

In this scenario, your assessed value increases, but it remains well below the replacement home’s full market value.

Example: Buying a less expensive home

• Original home: assessed value $350,000, current market value $700,000.
• Replacement home: market value $500,000.
• Calculation: $350,000 + ($500,000 − $700,000) = $150,000 assessed value on the replacement home.

If you buy down, your assessed value can decrease. You do not lose Prop 13 protection when you use portability.

What to expect on tax bills

After filing, you may receive supplemental assessments. These are one-time bills that true up differences between the old and new assessed values. Filing during escrow and keeping your lender and escrow officer informed helps align prorations and reduce surprises.

Sonoma County process: step by step

Sonoma County’s Assessor’s Office administers portability claims for replacement properties located in the county. The office reviews your eligibility, verifies market values, and issues a determination.

Follow these practical steps:

1. Confirm eligibility before or during escrow. Verify your qualifying status and confirm that both properties are or will be your principal residences.
2. Gather documentation. Collect records for the original and replacement homes, and documents that verify your eligibility.
3. Complete the county’s portability claim form. Submit the claim to the Sonoma County Assessor. Filing before closing or immediately after helps with processing.
4. Respond to any information requests. The assessor may ask for additional documentation or perform a field check.
5. Watch for your notice of value. The county will issue the adjusted assessed value and update your tax billing accordingly.

Documents checklist

• Deed or grant deed for your original property.
• Recent property tax bill showing original assessed value.
• Purchase contract and closing or settlement statement for your replacement property.
• Proof that the original property was your principal residence and that the replacement will be your principal residence, such as a driver’s license or voter registration.
• Proof of eligibility: photo ID for age, or a physician’s certification for disability.
• Disaster documentation if applicable, including records that the event was officially declared and that the home was uninhabitable.

Moving from another county to Sonoma

Intercounty transfers are allowed. If you are moving to Sonoma from another California county, file your portability claim with the Sonoma County Assessor. Sonoma may coordinate with your prior county to confirm the original assessed value and other details.

New construction as your replacement home

If your replacement residence involves new construction, supply completion documents. The county may use the completion date as the trigger for timing. Ask the assessor how to sequence your claim if you are buying land first and building later.

Smart timing in your transaction

Start the portability conversation as soon as you go under contract. Let your lender and escrow officer know you plan to file, since the assessed value affects tax prorations but does not usually change your loan approval.

Build in time for assessor review. Counties verify market values and eligibility, which can take time, especially around tax roll periods. Filing early gives you a better shot at having the correct assessed value reflected on your first tax bill.

Run the numbers. Use the examples in this guide to sketch a rough estimate of your post-transfer assessed value. Then confirm with the Sonoma County Assessor or your tax professional so you know what to expect for cash flow.

Common Sonoma move scenarios

• Moving from San Francisco to Sonoma. If you are 55 or older, severely disabled, or a qualified disaster victim, you can bring your base-year value with you. File the claim in Sonoma County after you purchase the replacement home.
• Selling in Sonoma and buying elsewhere in California. Portability follows you statewide. You would file with the assessor in the county where the replacement home is located.
• Rebuilding after wildfire. If your prior principal residence was destroyed or made uninhabitable by a declared wildfire or other disaster, you may qualify for portability. Gather your disaster documentation early and coordinate with the assessor on timing.

Limits and how often you can transfer

Most eligible homeowners can transfer their base-year value a limited number of times. Current county guidance commonly references up to three transfers for eligible homeowners. Because local practice and state implementation details can evolve, confirm the current limit and any exceptions with the Sonoma County Assessor before you rely on multiple transfers.

Pitfalls to avoid

• Waiting too long to file. There is a filing window tied to your purchase or construction completion. File during escrow or right after closing to stay on track.
• Assuming non-primary homes qualify. Investment, rental, or vacation homes do not qualify for portability.
• Forgetting documentation. Missing proof of principal residence or eligibility can delay processing.
• Ignoring supplemental assessments. Plan for possible one-time adjustments, especially if your replacement home’s market value is higher than your original home’s value.

Your next step

If Sonoma is calling, put a simple plan in place. Confirm your eligibility, gather your documents, and coordinate your filing timeline with the Sonoma County Assessor around your closing date. The right preparation helps you capture the benefit of Prop 19 portability and move with confidence.

Ready to map your move and line up the paperwork so your taxes follow you, not the market? Get strategic guidance, escrow coordination, and negotiation that protects your goals. Get More with RealWise. Connect with Unknown Company to start a clear, efficient path to your Sonoma home.

FAQs

Who qualifies for Prop 19 portability in Sonoma County?

• Homeowners who are 55 or older, severely and permanently disabled, or whose prior principal residence was made uninhabitable by a qualifying disaster. Both homes must be your principal residences.

How does the Prop 19 tax base transfer calculation work?

• The county takes your original assessed value and adjusts it by the difference between the replacement home’s market value and the original home’s market value. If you buy up, the difference is added. If you buy down, the assessed value can decrease.

When should I file my Sonoma portability claim?

• File with the Sonoma County Assessor during escrow or right after closing. Many counties note a filing window of up to three years, but you should confirm Sonoma’s current deadline.

Can I transfer my base-year value from another county to Sonoma?

• Yes. Intercounty transfers are allowed statewide. You file the claim in Sonoma County for your replacement home, and Sonoma may coordinate with your prior county.

Do investment or vacation properties qualify for Prop 19 portability?

• No. Portability is for principal residences only. Both the original and replacement homes must be your primary residences.

How many times can I use Prop 19 portability?

• Most eligible homeowners are limited in the number of transfers, and guidance commonly cites up to three. Verify current rules and any exceptions with the Sonoma County Assessor.

Will I get a supplemental tax bill after filing?

• You may receive supplemental assessments that reflect the change between your old and new assessed values. Filing early and coordinating with escrow helps manage timing and expectations.

What documents do I need for the Sonoma Assessor?

• Typical items include deeds, prior tax bill, purchase and closing statements, proof of principal residence for both properties, proof of age or disability, and disaster records if applicable.