How to estimate end buyer's profit?

[Trevon Peracca]

Does anyone have tips on how to accurately estimate what the end buyer's profit should be? 

I normally just estimate $25,000.00, but i know that there has to be a better way. If i was a rehab-er and paid cash for the property, paid $75,000 in repairs, plus holding for 4-5 months, i think id want more than 25k? 

Thoughts?