What should I do when I don't know the spouse income while file for "married file separately"?

[rjs]

If you are filing as married filing separately you do not need to know your spouse's income unless you are in a community property state. The community property states are Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington, and Wisconsin.

[kde]

But i'm in state CA.  the spouse hasn't yet filed tax return by 4/15 deadline. what can I do to complete my tax? do i need to file extension too?

[MarilynG1]

You could.  You also need to know whether your spouse is itemizing or not, so you can do the same.  You could probably start preparing your return, estimate their income, and enter your half of deductions to get an idea of what you should pay (if anything) when filing your extension. 

You can also pay at the IRS site, which gives you an automatic extension.  

@Le_aiphuong