I didn't use any formula, just logic. My home has been dropping in "value" about 1.8% a month for 3 months now, and we haven't even started a housing crisis. I figure that to be about 10X's what its been.What I did to come up with that figure was to take a $400k loan 20% down, at 4% was roughly a $1500 payment, and then worked backwards, reducing the value of the home until arriving at a similar payment, but at a 12% interest rate. That resulted in a home loan starting figure of 180k, and the difference between the two was how I got 55%
Again, my adult kids, my wife and I all own our homes outright, so it's not something I fret about. I just feel so bad that so many people are going to get blindsided when the shtf.
Bottom line, I'm a frugal dude. My motto has always been, "people buy when things are good and many times have to pay back when times are bad." I avoid that like the plague.
Off topic. Now we have millions of citizens doing the BNPL (buy now, pay later) short-term credit in the purchase of food. They can buy now, pay 25% of the total cost and put the other 75% off for 3 months. It's kind of a payday loan scenario for those who are financing the food they eat. Bad deal.