They are related but different: the lender's quote covers your ongoing taxes, and the supplemental bill is a one-time catch-up. In California this comes down to a Proposition 13 quirk. Assessed value can only rise about 2% a year while you own, so a longtime owner's tax bill often sits far below the home's market value. Your lender's quote should be based on your purchase price and your new, higher assessed value, which is what your escrow account collects for. The wrinkle is timing. The county does not reassess instantly when you buy, so for a while the tax collector keeps billing the prior, lower amount, and the servicer pays that lower bill from escrow. When the county catches up and reassesses to your price, it sends a supplemental tax bill covering the difference for the period in between. That supplemental bill often is not routed to the servicer automatically. Make sure a copy gets to them, ideally to someone who handles California accounts, so it gets paid before it goes delinquent. So your lender's quote should already reflect the correct ongoing taxes. The supplemental is a one-time bill for the gap, and your taxes do not stay at that combined level. Confirm the details with your lender and county so nothing slips.