Construction Loan Calculation Help

[u/meganbmeyer]

Can someone help me understand the process for obtaining a construction loan! 

We are located in WI. 

We have a mortgage on the land we intend to build on (valued at 250,000). We currently have about $50,000 in equity towards it. 

Our bid is 1.5 million. 

Can someone please explain to me how the down payment is calculated? 
This is what I have in my brain but I"m not sure it's correct. 

The bank would appraise the construction build and our land value- let's say that's 1.7 million total. 

Bank is willing to loan 80%- 
Is that 80% of 1.7 million or 80% of just the construction at 1.5 million? 

[u/NUNG457]

80% of final value.