# San Francisco Supplemental Tax Bill Calculator (2026) · The Rent Hacker > Estimate the supplemental property tax bill you get after buying in San Francisco: the Prop 13 reset, the proration by closing month, and why a January to May closing brings two bills. Uses the rate the city actually charges. Canonical: https://therenthacker.com/san-francisco-supplemental-tax-bill-calculator/ Source: The Rent Hacker (https://therenthacker.com/). License: RSL, attribution required — https://therenthacker.com/license.xml --- Calculator # How much will your San Francisco supplemental tax bill be? When you buy in San Francisco, the assessor resets the property's taxable value to your purchase price. The regular tax bill keeps running at the seller's old value until the next roll, so the county sends a separate bill for the difference, prorated for the months you own the place this fiscal year. That is the supplemental bill. Your lender's escrow was set up from the seller's old bill, so it usually does not cover this one. Plan to pay it yourself. ## What you can expect Buying at $1,200,000 on a $650,000 assessment, closing in March 2026: the supplemental value is **$550,000**, taxable from **April 1, 2026**, and you should expect **two bills** totaling **$8,130.95**. Bill Fiscal year Months owned Taxable value Amount First 2025-26 3 of 12 (25%) $137,500 $1,626.19 Second 2026-27 12 of 12 (100%) $550,000 $6,504.76 When it arrives Within 60 days of the assessor's Notice of Supplemental Assessment, which itself follows the recorded sale by some weeks. Budget for it in your first few months. Your regular bill after this About $15,563.42 a year at the new value: $14,192.20 at 1.18268325%, plus roughly $1,371.22 in fixed parcel charges (the median of 10 measured San Francisco bills; your parcel's own charges are on its bill). That is about 1.3% of the price, rising 2% a year under Prop 13. You are buying below the seller's assessed value. The county issues a supplemental refund for the difference, not a bill. ## How the number is built 1. **The supplemental value is your price minus the seller's assessed value.** The assessor "subtracts the property's prior assessed value from its newly assessed value. The difference between the two is the supplemental value." [SF.gov, supplemental assessments](https://www.sf.gov/information--learn-about-supplemental-assessments) 2. **It is prorated by the months left in the fiscal year, starting the first of the month after you close.** The fiscal year runs July 1 to June 30. Close in March and the value is taxable from April 1, which leaves 3 of 12 months, so the first bill is 25% of a full year. Close in July and it is taxable from August 1, 11 of 12. [California BOE proration table](https://www.boe.ca.gov/proptaxes/supplemental-assessment/), Revenue and Taxation Code sections 75 to 75.72 3. **Close between January 1 and May 31 and you get two bills.** The first covers the rest of the current fiscal year. The second covers the entire next fiscal year, because that year's regular bill was already calculated on the old value before your sale recorded. Close June 1 through December 31 and there is one bill. [SF.gov](https://www.sf.gov/information--learn-about-supplemental-assessments) A purchase below the seller's assessed value works the same way in reverse: the county issues a refund instead of a bill. ## What this does not cover - New construction and remodels, which trigger their own supplemental assessment on a different timeline. - Reassessments that are not sales, such as a change in ownership through a trust or an inheritance with an exclusion. - Your parcel's exact fixed charges. The figure above is a median from measured bills; the real ones are itemized on the seller's bill. - How your specific lender handles escrow. Most do not collect for the supplemental bill; ask yours before closing. To model the whole purchase, rent and all, run it through the [house hacking calculator](/calculator/). For the neighborhoods and buildings we underwrite in the city, see the [San Francisco guide](/house-hacking/san-francisco/). ## Want this for an address you pick? Every week we underwrite this metro’s 2-4 unit listings against the S&P and publish the [whole board](/board/), with the reason on every one we rejected. [Or look up a specific San Francisco address](/lookup/) ## Want this analysis for another address? Any San Francisco address, underwritten the same way — cautious rents, the registry, the S&P line. [Underwrite an address →](/lookup/) A full report like this one, for an address you pick: Underwrite an address — $79, delivered within one business day.