Your mortgage estimates are crap. If their mortgage $600k @ 4.25% they will make principle+interest payments of $2,950/mo. The first year they will pay down $

Your mortgage estimates are crap. If their mortgage $600k @ 4.25% they will make principle+interest payments of $2,950/mo. The first year they will pay down $10k in principle. Year 10: $15.5k Year 16: $20k So, unless they had the huge house many years before they had kids they are only "buying" 10-15k of house.