Well given what I see on eBay, and using that as my only guide, I would suggest that for a tractor 0 to 3 years old from a Big 3 brand, the depreciation should be 5%, perhaps a bit less. I would also suggest that for a tractor 0 to 3 years old from any other brand, the depreciation should probably be closer to 20%. (assuming in both cases the tractors are garaged, dent free)
Now at roughly 4 to 6 years old I think the depreciation may start to level out a bit. And at 6 years or more, perhaps your formula might be pretty darn accurate.
I'm just guessing, but I would suspect that $14,500 is probably pretty close to the original price of the Mahindra? And since there are no bids with 5 hours left on the auction, one of two things is going on. Either it is not worth the $11,000 asking price, or people are waiting to the last minute to bid in hopes of getting it at that price because if it gets bid up in price it probably is overpriced.
If you go up to your formula and my price assumptions, but substitute a 20% depreciation for the tractor, the calculation would leave the 'value' at $11,038.
Now if my original price is too high, and if the original price was closer to $13,500, then the numbers would be slightly different on the depreciation and the fuel/hour, but correspondingly the value would drop as well. Using your original formular, the 'value' would be $11,588 but using a 20% depreciation rate, the 'value' would drop to $10,238.
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Brian, here are the numbers for the 2004 CK30 that is on auction at eBay now. Again, no bids, 1 year old tractor. $15,000 presumed original price (based on prices quoted over on TBN for this machine).
$15,000
- $1500 depreciation (your 10% model)
- $450 ($3.75 per hour)
- $240 wear and tear
= $12,810 value for the Kioti
The auction lists a "Buy It Now" price of $13,750 and a starting bid of $13,000.
Now if we modify the depreciation to 20%, the tractor would be worth about $11,310.
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Now compare all that to my 2 year old/190 hour New Holland TC24, with an orignal price of $13,300 (tractor & loader) and a recent offer to buy it for $13,300 (the offer was from one of the dealers I buy tractors/implements from, so I presume they would resell it for more money).