Property Tax Doubled at Purchase

[Tim Shi]

Hi there, I am looking at a Duplex in San Francisco. The current owner pays about $500/mo on property tax. The property was sold in 1999 for less than half a million. The assessed value of the property doesn't seem to go up that much despite the rapid increase in fair market value. 

The house is now valued at 1.5 million. Based on the current tax rate of 1.18% in San Francisco, the new property tax would be $1475 / mo.

Is my calculation correct? Basically there will be a 1k jump in property tax at sale.