San Francisco owners: sign up by Monday, September 14 at 5 p.m. Pacific.

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1011 23Rd St owners: lower your property tax.

1011 23Rd St, San Francisco. We review your assessment and handle your appeal. You pay only if we win.

Sign up your unit →

About 5 minutes. Sign up by Monday, September 14 at 5 p.m. Pacific — 2 days left.

1011 23Rd St at 1011 23Rd St, San Francisco

Your assessment should reflect the market.

A building's market can change while individual assessments stay high. We check your unit's assessment and tell you whether there is a case for a reduction.

What an appeal could save

Average potential first-year savings, after our service fee $1,100

An estimate, not a promise. Average for the 7 homes flagged in our 2026 building review, rounded down, after our standard service fee and before county costs. Uses the proposed tax rate. Your unit's savings can differ.

From sign-up to decision

01

Sign up online.

Your building is already filled in. Add your unit, confirm your property, and sign the California agreement and authorization online by Monday, September 14 at 5 p.m. Pacific.

02

Review your assessment.

We review your unit's assessment and the available evidence to determine whether an appeal makes sense.

03

File with San Francisco.

If there is a case, we prepare and file your application with the San Francisco Assessment Appeals Board by September 15, 2026, and advance the filing fee.

04

Build the case for your unit.

We gather the property records and market evidence needed to support a lower assessed value.

05

Negotiate with the Assessor-Recorder.

We present the case to the assessor's office and work toward a reduction before a hearing.

06

Represent you at the hearing.

If a hearing is needed, we present your evidence to the Assessment Appeals Board or hearing officer and follow through on the decision.

You sign up. We handle the appeal.

What you pay, and when

  1. Nothing now, and nothing if we don't win.
  2. When you sign up, save a card or US bank account. Autopay earns a credit of 2% of our fee — for every $100 we charge, you pay $98.
  3. If we win a lower assessed value, your property tax falls with it.
  4. Then we charge 35% of the tax savings for the year, plus county fees we advanced at cost, with a heads-up email first. Our rate falls to 30% when your combined assessed value exceeds $5,000,000. Nothing on file? We email the bill, due in 30 days.
Sign up your unit →

Own more than one unit?

Add your units to the same signup, including homes in other buildings. Each property keeps its own assessment and appeal.

Talk to us

Questions

Can I appeal myself?
Yes. You can request a free informal review directly from the Assessor-Recorder or file your own application with the San Francisco Assessment Appeals Board. Castellan is a private service, independent of government.
What do I need to sign up?
Your unit number, your contact information, and the authority to sign for the owner. We look up the property record. If we need documents for the case, we will ask for them.
My unit is in an LLC or trust
Sign as the person authorized to act for that owner and enter the ownership details in the signup form.
Will every unit get a reduction?
No. Each unit has its own assessment and evidence. A low existing assessment or resale restrictions can change whether an appeal is worthwhile. We review the unit before filing.
Does a reduction last forever?
A California decline-in-value reduction is reviewed annually. Future assessed values can rise again, up to the Proposition 13 protected value. The agreement explains how future-year reviews and fees work.
Does this change HOA dues?
No. This service concerns property tax assessments, not HOA dues or fixed charges on your tax bill.
California service disclosure
THIS ASSESSMENT REDUCTION FILING SERVICE IS NOT ASSOCIATED WITH ANY GOVERNMENT AGENCY. IF YOU DISAGREE WITH THE ASSESSED VALUE OF YOUR PROPERTY, YOU HAVE THE RIGHT TO AN INFORMAL ASSESSMENT REVIEW, AT NO COST, BY CONTACTING THE ASSESSOR’S OFFICE DIRECTLY. IF YOU AND THE ASSESSOR CANNOT AGREE TO THE VALUE OF THE PROPERTY OR IF YOU DO NOT WISH TO CONTACT THE ASSESSOR YOU CAN OBTAIN AND FILE AN APPLICATION FOR CHANGED ASSESSMENT WITH THE COUNTY BOARD OF EQUALIZATION OR ASSESSMENT APPEALS BOARD ON YOUR OWN BEHALF. AN APPEALS BOARD HAS THE AUTHORITY TO RAISE PROPERTY VALUES (BUT IN NO CASE HIGHER THAN THE PROPOSITION 13 PROTECTED VALUE) AS WELL AS TO LOWER PROPERTY VALUES.

Keep paying your property tax bills while the appeal is pending. Filing an appeal does not suspend payment deadlines.

Your unit at 1011 23Rd St.

Add your unit and we take it from there. Sign up by Monday, September 14 at 5 p.m. Pacific. The county's filing deadline is September 15, 2026.

Sign up your unit → Book a 15-minute call
Text or call(470) 912-3429 Emailinfo@castellan.so

Questions? Text us or book a call.

Castellan is a private company, not a government agency. Potential savings are estimates, not a promise.