Lenders appraisal is there a formula they follow to approve loan

[Susan K.]

Question for any lender/underwriter:

If someone is getting a conventional loan, (borrowing 80% for example) if the appraisal comes back less than the contracted price, but hits at least the 80% mark would this get approved by underwriting?  Is there a formula they follow that you need to hit above a certain % of the amount borrowed to get approved?

I hope my question makes sense.  Thanks