When you own rental property, one of the expenses that you claim each year is depreciation on the property. Commercial rental property is depreciated over a period of 39 years. So if you paid $162,000 for this property, then you should have claimed a depreciation amount of $4,154 each year ($162M divided by 39). Since you purchased this property 44 years ago, then you would have fully depreciated the property by now, so that has to be figured in to your capital gains.
The repairs, real estate taxes and insurance premiums you paid over the years would not figure in to this, because those should have been expensed each year. To figure your gain on rental property, you need to take the selling price, less your basis.
Your basis in this property is the $162,000 that you paid for it plus the $135,000 you made in improvements, or a total of $297,000. Now you need to deduct from this the depreciation you claimed, which should be the full $162,000 since you have owned the property for more than 39 years. So your basis is now reduced to $100,000.
If you sell the property for $650,000, you deduct your basis and have a gain of $550,000.
On that gain of $550,000, the $162,000 that is attributable to your depreciation recapture is taxed at a special rate of 25%. The remaining gain of $388,000 would be taxed at the long term capital gains tax rate of 15%. So I would estimate your total tax on the sale to be $98,700.
You will need to check your actual depreciation figures as you may have claimed additional depreciation for the improvements you made, and I would have no way of calculating that amount since I do not know when those improvements were made and how much depreciation you may have claimed up until this time.
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