Thank you for the response.  I never considered this, but I’ve had a hard time finding a definitive approach.  When you say total miles, are you referring to just business miles or everything?

This is what I had considered doing (simplified example):

Basis at time of conversion - $20,000

Trade-in Value - $10,000

Average business use since conversion – 5%

Business portion of trade-in price - $500

Adjusted basis = Business Cost Basis – Depreciation = ($20,000 x 5%) - $225 = $775

Loss = $225