My employer under withheld both Fed and CA tax and I owe a significant amount. Do I still get the same safe harbor rules if I pay nothing on my extension filing?

[susanengquist64]

I paid in for both CA and Fed 100% of my 2017 tax liability

[MichaelL1]

The extension is for filing taxes only not for payment.

When you do an extension you need to pay the taxes that you think are due or you can get a penalty for failure to pay plus interest.