I’m looking at buying a truck for our business (80% biz/20% personal use) and understand the big picture of how it works. What I don’t understand is whether or not or matters if I finance the car.

If I put $10,000 down on a new truck, do I still get the $18k write-off (at 80%) or only the down payment. And then how are the monthly payments treated? Are they also expensed each month or do you just take the depreciation figure each year?