@Brandon Bellino This is how I was taught to calculate my seller financing offers when I send an LOI:
I always offer 3 options - two with seller financing and one cash option.
Formula: ARV=NOI using actual rent amounts/market cap
This gets me the retail value of the property if it were all fixed up and occupied and this number also equals my Option 2.
Option 1 is 100% seller financing at 5% interest. It is typically a 3% to 6% higher offer than option 2 (this is based on ensuring that the property will support the payment). This is always an appealing number since you're giving the seller the interest over time and they sometimes end up making more than their original asking price.
Option 2 is the formula I worked out above. I offer 15% down and 85% seller financing at 5% interest for this option.
Option 3 is all cash to the seller through traditional 3rd party financing and 25% down. This option is roughly 17% less than option 2.
Just make sure that no matter what the offer is that the property can support the payment.
Good luck!