I'm filing MFS (i'm in divorce). In CA capital gains are split 50%. If spouse doesn't pay his share, will the IRS hold me responsible for 100%? is it a JOINT liability?

[junklen]

While in divorce in CA, we sold our marital home and have capital gains. We separated 4 months ago, but legally are still married in 2016. We will file "Married Separately" (MFS). I know that each pays 50% of capital gain taxes and each will take the qualified $ 250,000 deduction. However, if my spouse doesn't pay his share of the capital gain tax, will I be liable for 100%? How do I protect myself? How would the IRS consider the tax liability: Joint or separate?

[Opus 17]

You should be protected by MFS.  When you report the sale, report half the basis and half the sales price to calculate half the gain.  

If no 1099-S was issued, that should be all you need to do.  If a 1099-S was issued and your SSN was listed first, then you might get a letter requesting more information.  But you can answer that.