Need clarification on a 1031 exchange term

[Lisa R.]

Hello – I am considering doing  a 1031 exchange on a property I own. I am trying to reduce the boot as much as possible.  I understand that when you purchase the replacement property, any difference between the value of your current property and the one being replaced will be taxed. If I am wording this incorrectly – you know what I mean :)

This is my question: when they consider the ‘value’ of my current property, does that mean what my current property is ‘worth’?  Or the amount that I am selling it for?

The reason I ask is because I am selling it for less than the market value. So I am assuming they will take the current fair market value of the property? 
I cannot thank anyone enough who chooses to answer this for me! I cannot find it anywhere online. Common sense tells me it is the market value of the property but I’m just not sure… 

Thank you so much!! 
Lisa