For California, is there an advantage prepaying 2019 property tax in 2018. Is there a limit in 2018 tax year for property tax deduction?

[DoninGA]

For tax year 2018 and beyond State, Local, property and Sales Tax (SALT) deduction are limited to $10,000 ($5,000 if Married Filing Separately.  So if you prepay the 2019 property tax in 2018 and that payment increases your total SALT deductions to greater than $10,000 then only $10,000 can be deducted.

See this TurboTax support FAQ for how tax reform affect your 2018 tax return - https://ttlc.intuit.com/questions/4482394-how-will-tax-reform-affect-my-2018-federal-tax-return