The rules are similar for the FSA. The maximum amount of FSA that you could use tax-free is $5000 or your wife's earned income, whichever is lower. If you are expecting that she might have income in 2017, you could sign up for the FSA now. If she ends up having no earned income of her own, you are not eligible to use an FSA and the amount spent on care will be added back to your taxable income. But there is no penalty. So if she might have income, you could do the FSA just in case, and if she ends up not having income, then you are no worse off than just not doing it.
