When purchasing real estate, including residential real estate, buyers might be fortunate enough to not only purchase a home they love, but they may also come to find they have purchased some “built in equity”, as well. In short, built in equity is the difference in what is paid versus what the home is actually worth (at the time of purchase) AND presumes that the purchase price was LESS than the market value.
An example would be as follows: Someone purchases a home for $250,000 that is arguably worth $300,000. In this scenario, the built in equity is $50,000. This is pretty straight forward. It is very much the same as when someone purchases some pretty looking bowl at a flea market, only to find out later that the $25 purchase price actually bought that person a $5,000 antique.
So, instead of “Antiques Roadshow”, it is “Real Estate Roadshow”.
Still, you wonder “What is ACHIEVABLE Built in Equity?”. House “flippers” do this calculation all the time. This type of equity is equity realized AFTER remodeling money is put into a recently purchased house, wherein the sum of the purchase price AND the remodeling money is LESS that the ultimate, remodeled value of the home. 
An example of this would be as follows: Buyers purchase a home for $100,000. Given the shape it is in, It is pretty much worth $100,000. Much of the work to be done is cosmetic. Some is functional, such as needing a new HVAC, windows and roof. Some is cosmetic, such as updating the kitchen.
However, this home is located in a neighborhood where similar homes, though updated, achieve over $200,000. A remodeled house like the subject house could potentially fetch $175,000. The amount of money to bring the house up to “speed” is $35,000. So, the house has “achievable” built in equity of $35,000.
The point here is that even the typical home buyer, looking for a home in which to live, should still be sensitive to this type of investment potential. Ultimately, home buyers are looking for a place where they are going to love to live. Yet, it doesn’t hurt to add a little $$$ equity to the equation.