Los Angeles County Supplemental Tax Calculator
Estimate supplemental property taxes for Los Angeles County after a change in ownership or new construction. Defaults to the Countywide 1.00% general levy; you can override to include voter‑approved debt for your Tax Rate Area.
Estimate
Bill #1 – Current fiscal year
Bill #2 – Next fiscal year
How this estimate is computed
- Compute Net Supplemental Assessment = (New Assessed Value − Prior Assessed Value − Exemptions).
- Set the Effective Date to the first day of the month after the event date.
- Find the Proration Factor based on the Effective Date month (Jan 1 → 0.50, Feb 1 → 0.42, Mar 1 → 0.33, Apr 1 → 0.25, May 1 → 0.17, Jun 1 → 0.08, Jul 1 → 1.00, Aug 1 → 0.92, Sep 1 → 0.83, Oct 1 → 0.75, Nov 1 → 0.67, Dec 1 → 0.58).
- Bill #1 = Net × (Current FY rate) × (Proration Factor).
- If the event date is between Jan 1 and May 31, a second full‑year supplemental (Bill #2) is estimated as Net × (Next FY rate) × 1.00.
- Negative totals indicate a refund (when the new value is lower than the prior value).
This tool estimates the ad valorem portion only (1% base rate plus voter‑approved debt). It does not include direct/special assessments such as fixed‑charge districts or Mello‑Roos (CFDs), which typically are not part of supplemental bills. Actual tax rates and factors are set by your county auditor‑controller.
This calculator is for informational purposes only and not a tax bill. Default rate reflects LA County’s 1.00% general levy; voter‑approved debt varies by Tax Rate Area. For the most accurate estimate, replace the rate with the total ad valorem rate shown on your most recent secured bill.