Letâs look at a hypothetical spontaneous chemical reaction: The quantity of usable energy (chemical potential) in a reaction is called the Gibbs Free Energy (DG). DG is the difference between the energy contained in the products of a reaction and the reactants: DG = (energy of products) - (energy of reactants)
That's why some financial experts feel it's more realistic to think in terms of your net income, aka take-home pay, and that you shouldn't use any more than 25% of your take-home on your mortgage payment.
1 A homeowner will pay more than $179,000 in interest alone for a 30 year mortgage on $250,000 at 4% interest, so the total cost will be closer to $429,000. 2  Furthermore, this figure does not include insurance and maintenance costs.