# depreciation in income approach of GDP

I have some doubt regarding gdp sector, while measuring gdp by income approach, we add depreciation. My doubt is: does the cost of goods that go into replacement of existing worn out capital is only treated as depreciation? Or do we also add the depreciation expense of all existing and serving goods, which have not worn out?

Lets imagine a hypothetical scenario where you buy a capital good of a tractor. The tractor will cost $100 and last 10 years. On the tenth year you know that the tractor will explode and be completely worthless and useless meaning you'll have to buy a new tractor for $100. Under GAAP accounting you don't record that the tractor suddenly became worthless on the 10th year. Instead you estimate in the beginning the overall lifetime of the tractor and divide that by the cost of the tractor. Thus, the tractor will depreciate by \$10 every year. You do this because it is a better indication of the value of the asset(capital good) you have left of the tractor despite the fact that the tractor may work perfectly fine for all 10 of those years.