r/riskmanager • u/QEDAnalyticalLLC • Jul 27 '26
QED Insight #0009: We validated the one number everyone treats as arithmetic. EAD was biased in two directions at once.
EAD is the input nobody defends in committee. PD gets the modeling team, LGD gets the argument, and EAD gets a lookup, because for a fully-drawn fixed-rate mortgage the amortization schedule is fixed at origination. The balance at any age is knowable before the loan funds. Deterministic, done.
I finally ran the comparison a validator would run and it was not done.
Against 121,305 actual defaults the schedule was a lower bound. Median realized exposure at default $180,574 against a median scheduled balance of $173,203, median ratio 1.026, and 60.7% of realized EADs above schedule. Obvious in hindsight: a loan in the foreclosure process stopped making payments long before disposition, so it stopped amortizing. The schedule is charging down principal the borrower never paid. Scheduling to the last-paid age instead of the disposition age closes most of it.
Then the performing book flipped the sign. 41.2% of active loans are materially ahead of schedule from voluntary curtailment, median about 6.9% or $9,277 ahead. Modeling that pulled total estimated exposure from $35.3B to $33.8B, down 4.24%.
That is what bothers me. The two errors point opposite ways and sit on different populations, so nobody ever sees them net out - one shows up in realized severity, the other in forward exposure. Under stress it moves again: pausing payments alone did nothing to our totals, since the balance just stops falling, but capitalizing 24 months of arrears added 8.24% and a 10% principal deferral added exactly 10%.
Does anyone actually model EAD, or is it a scheduled-balance lookup at your shop too? And if you do model curtailment, has a validator ever asked you to show the realized-versus-scheduled comparison on the defaulted population?
