taxes on the sale of a 12 unit apartment

[Julie Kalar]

hello i am looking a purchasing a 12 unit apartment in olympia, wa. The current owner bought it for 625000.00 25 years ago, she hasnt done any maintenance to it and i am looking at asking 850000.00 with owner financing. I am trying to get an idea of what she might pay in taxes. So i can come up with a down payment that will cover her taxes. I know that there are many things that can effect this. Her tax rate, if she depreciated over the last 25 years. what would be the worst case scenario?