Prop 13 caps how much your property tax can rise each year once you own the home — but it does nothing to soften your first bill. The county assessor resets your basis to the actual purchase price the moment you close, and if that price is well above the seller's decades-old basis, a separate, prorated "supplemental" bill for the difference arrives on its own timeline, months after the sale, and it isn't the number most buyers budgeted for.
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Talk to a Specialist →This isn't a fee anyone is hiding — it's public record, and every county publishes an estimator. But it rarely comes up in the excitement of a purchase, and buyers moving from a non-reassessment state have no frame of reference for it at all. The bill isn't optional and isn't cancelled by Prop 13; the 2% annual cap only starts protecting you the year after this one-time reset already happened.
You buy in Placer County at $640,000. The seller's Prop 13 basis was $350,000. The taxable difference is $290,000. Closing in October leaves roughly 8 months in the fiscal year — a proration factor of about 0.67.
0.67 × $290,000 × 1.12% (Placer's effective rate) ≈ $2,178 — a one-time supplemental bill, separate from your regular installments, typically due within a few months of closing.
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| Community | County | Effective rate |
|---|---|---|
| Sun City Lincoln Hills, Sun City Roseville, Springfield at Whitney Oaks | Placer | ~1.12% |
| Heritage Park, Four Seasons at Westshore | Sacramento | ~1.19% |
| Four Seasons at the Ranch | Sacramento (Rancho Cordova) | ~1.23% (highest in metro) |
| Four Seasons at El Dorado Hills, Heritage El Dorado Hills | El Dorado | ~1.15% |
The gap between the seller's basis and your purchase price is what actually drives the supplemental bill's size — a higher effective rate matters, but the reassessment gap usually matters more, especially on a home that's changed hands rarely or sat with a long-time owner. Ask any listing agent directly for the seller's current assessed value, not just the asking price, and run the estimator on your own state's county assessor site before you close, not after.
The honest way to shop this market: before making an offer, ask for the seller's current assessed value and run the supplemental-bill math yourself using your target county's estimator — the sticker price and the HOA fee are not the whole first-year cost picture in California.
Connect with a specialist who knows this market from the inside — real cost math, honest community comparisons, and what's actually happening right now. Every agent is personally vetted by the Nova55Living founder.
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