For 2016 Roth IRA the rules state that:  

 Greater than $193,000 - Ineligible for a Roth IRA

Let's say someone makes $200,000 pre-tax salary and wants to contribute 
$5,500 to Roth IRA in early January 2016. How do they know if they can or can't contribute if their Adjustable Gross Income has not yet been calculated.

So, what happens if you contribute $5,500 in 2016 and then when taxes come around in 2017 you find out that you were ineligible?