The California Supplemental Property Tax Bill New Homeowners Don't Expect

You closed on a California home. Your monthly payment includes an impound account for property taxes. Then, sometime in the following months, an unexpected tax bill arrives in your name — often for a substantial amount, and often with a due date that does not line up with anything you were told at closing.

This is the supplemental property tax bill. It is not an error, it is not a scam, and in most cases your lender will not pay it for you.

Key takeaways

• A supplemental bill is triggered by a change in ownership or completed new construction, which causes a Proposition 13 reassessment.
• It is governed by California Revenue and Taxation Code sections 75 through 75.72.
• The bill covers a prorated period: from the first day of the month following the event through the end of the fiscal year.
• If your purchase closes between January 1 and May 31, you may receive two supplemental bills instead of one.
• Lenders do not receive the supplemental bill. California law sends it directly to the property owner.

Why it exists

Under Proposition 13, a property's assessed value is generally limited in how much it can rise year to year — until there is a change in ownership or new construction, at which point the property is reassessed at its current value.

The problem is timing. County assessment rolls are prepared well in advance, so a home that sells in, say, September is still on the roll at the previous owner's assessed value, which may be far lower after years of Proposition 13 limits.

The supplemental roll is the mechanism that fixes this. As the California State Board of Equalization describes it, the supplemental roll "provides a mechanism for placing property subject to Proposition 13 reappraisals due to change in ownership or completed new construction into immediate effect."

Rather than wait until the next annual cycle, the county bills you for the difference right away.

How the amount is calculated

The county assessor determines the new base year value of the property as of the date of the event, and compares it to the value already on the roll. The difference is the supplemental assessment.

That difference is then prorated. The supplemental bill "covers the period from the first day of the month following the supplemental event to the end of the fiscal year," with monthly proration factors applied to calculate the tax owed.

The practical consequence: the size of your supplemental bill depends heavily on two things — how much the assessed value increased when you bought, and what month you closed. A purchase early in the fiscal year is prorated across more months than one late in the year.

Why some buyers get two bills

This is the part that surprises people most.

If the supplemental event occurs between January 1 and May 31, two supplemental tax bills or refunds are issued. One bill covers the remainder of the fiscal year in which the event occurred; the second covers the following fiscal year, which has already been established on the roll at the prior value.

If the event occurs between June and December, a single supplemental bill is issued.

So a buyer closing in, for example, March should plan on two bills, not one.

The impound account trap

If your loan has an impound (escrow) account, you may reasonably assume property taxes are handled. For your annual bill, they generally are. For the supplemental bill, they generally are not.

The Board of Equalization is explicit: "Unlike the annual tax bill, lending agencies do not receive the original or a copy of the supplemental tax bill even if they are otherwise being sent and are paying the owner's annual tax bills." Supplemental bills are "sent directly to the property owner as stipulated by law."

Supplemental assessments are also not paid by the title or escrow company at close of escrow, and are not built into lender impound accounts.

What this means for you:

1. The bill comes to you, in your name. It is your responsibility to make sure it gets paid.
2. Do not assume your servicer saw it. They did not receive a copy.
3. If you want it paid from impounds, ask first. Contact your loan servicer when the bill arrives to confirm whether they will pay it and what they need from you. Policies differ.
4. Missing it has consequences. An unpaid supplemental bill becomes a delinquent property tax, with the penalties that follow.

How to plan for it before you close

You cannot avoid a supplemental bill, but you can avoid being blindsided by it.

• Estimate it in advance. Many California county tax collector and assessor websites publish supplemental tax estimators. Because the calculation depends on your purchase price, the prior assessed value, the local tax rate, and your closing month, an estimate is worth running before you finalize your budget.
• Set money aside at closing. Treat the supplemental bill as a known post-closing cost rather than a surprise.
• Watch your mail. The bill can arrive months after closing, well after you have stopped expecting closing-related paperwork.
• Ask your agent and your loan officer to flag it. A good file review should raise it before you sign, not after.

Our payment calculators can help you frame the ongoing monthly picture, and mortgage basics covers how impound accounts work generally. Keep in mind that a payment estimate built around the seller's current tax assessment will understate what you will actually pay once your property is reassessed.

Related California resources

For financing limits by county, see our California loan limits guide. If you are a first-time buyer, our CalHFA MyHome down payment assistance guide covers the state's assistance structure. Buyers weighing conforming versus jumbo financing in high-cost counties may find our Bay Area conforming vs. jumbo guide useful.

Local pages: Sacramento, Los Angeles, San Diego, SF Bay Area, and Orange County.

Questions about how a supplemental bill fits your budget? Browse our loan officer directory or get started.

Frequently Asked Questions About California Supplemental Property Tax Bill

What is a California supplemental property tax bill?

It is a one-time prorated tax bill issued when a property is reassessed because of a change in ownership or completed new construction. It covers the difference between the prior assessed value and your new base year value, from the first day of the month after the event through the end of the fiscal year.

Does my impound account pay the supplemental tax bill?

Usually not. California law sends supplemental bills directly to the property owner, and lending agencies do not receive a copy even when they pay your annual tax bill. Contact your loan servicer when the bill arrives to confirm who will pay it.

Why did I receive two supplemental tax bills?

If the change in ownership occurred between January 1 and May 31, two supplemental bills or refunds are issued — one for the remainder of the current fiscal year and one for the following fiscal year, which was already set at the prior assessed value. Events between June and December generate one bill.

When will the supplemental bill arrive?

Timing varies by county and depends on how quickly the assessor completes the reassessment. It commonly arrives months after closing, so keep watching your mail well after the transaction is complete.

Is the supplemental bill in addition to my regular property taxes?

Yes. Supplemental tax bills are in addition to the annual property tax bill, not a replacement for it.

Sources

• California State Board of Equalization — Supplemental Assessment overview
• California Revenue and Taxation Code sections 75 through 75.72

This article is for general information only and is not legal, tax, or financial advice. State law and investor guidelines change; confirm current requirements with a licensed professional before making decisions. Xpert Home Lending, Inc. is an Equal Housing Lender.