It's really a regional thing as far as who uses what valuation guide. In my area, NADA is soley used...some banks/lender's use Clean Retail for their guidelines and some use Clean Trade-in. Most CU's will also use NADA, It seem's very few national lender's in my experience use KBB which is why I honestly disregard their figures for the most part. NADA values are based off of auction sales, retail sales, and prices off of classified listings.
Most lender's will finance up to 110% of clean retail..some will even go up to 120%. I have seen national lender's finance as much as 135-140% of clean trade-in.... (never a good idea)
When calculating the equity/inequity I would go off of NADA clean-trade in value, as most dealer's when trading for a car will try to be somewhere under or around that value. Calculating equity off of retail values would only be useful if you are selling your vehicle privately, as a dealer will never give you retail value for a car as they have to leave room to profit off the next customer.
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