You bought a home, closed, and set up your mortgage escrow. Then, sometimes months later, a second property tax bill arrives that you weren't expecting — and your escrow account doesn't cover it. This is a supplemental or escape assessment, and it catches thousands of new homeowners off guard every year. Understanding it before it lands can save you a financial surprise.
Why the surprise bill happens
In many states, buying a home or completing new construction triggers a reassessment to current market value — often your purchase price. But the regular tax roll for the year was already set based on the prior owner's (lower) value. To capture the difference between the old assessed value and the new one, the county issues a separate, one-time bill for the portion of the year after your purchase or completion. Depending on the state, this is called a supplemental bill, an escape assessment, or a corrected/omitted assessment.
| Bill type | What triggers it | What it covers |
|---|---|---|
| Supplemental | Change of ownership or new construction (states like California) | The increase in value, prorated from your purchase/completion date through the rest of the tax year |
| Escape / omitted | Value that was left off or under-assessed in a prior year | Back taxes on the missed value, sometimes for multiple prior years |
| Corrected | An error on the original bill is fixed | The difference between the wrong and correct amounts |
California is the classic example: under Revenue & Taxation Code §75, a change of ownership or new construction triggers a supplemental assessment, and the county mails a supplemental bill for the prorated difference — completely separate from the regular annual bill. Roughly a dozen-plus states have a true supplemental mechanism; many others use escape or corrected bills to accomplish the same thing. Check the Property Tax Edge Supplemental Bills reference for your state's specific rules.
Why your escrow usually won't cover it
When your servicer set up your escrow at closing, it budgeted for the regular annual tax bill — not a one-time supplemental bill it had no way to predict. As a result, supplemental and escape bills are typically sent directly to you and are your responsibility to pay by their own due date. Don't assume your servicer will handle it; confirm in writing, and if you want, ask whether they'll pay it from escrow and re-analyze your account.
Ignoring a supplemental or escape bill because you 'already pay through escrow' is a common and costly mistake. These bills carry their own delinquency dates and penalties. Open every property tax notice and confirm who is responsible for paying it.
You can usually appeal a supplemental bill
A supplemental or escape bill is based on an assessed value — and just like your regular assessment, that value can be wrong. If the county's new value is higher than what you actually paid or higher than fair market value, you can appeal. Two things to know:
- The appeal window for a supplemental/escape bill is usually separate from — and often shorter than — the regular annual appeal window, and it runs from the date of the supplemental notice, not the regular assessment date.
- Your purchase price is powerful evidence. If you were reassessed above what you just paid in an arm's-length sale, that's often a straightforward reduction.
New buyers have the best evidence anyone can have — a recent, market-based purchase price. If your supplemental or first regular assessment comes in above your purchase price, appeal it promptly using the Property Tax Edge calculator and your closing documents.
Sources & currency: state supplemental/escape rules verified July 2026 against state statutes and revenue departments (e.g., California R&T Code §75). Rules, proration methods, and appeal windows vary by state and change over time — confirm the current rule for your state via the Supplemental Bills reference and your county assessor before relying on any specific timing.