@AuldFort - might be worth seeing an accountant and get some help. While the focus of this thread is the date of the estimated taxes and what the minimum is to avoid penalties, might be worth getting your hand around the tax actually due - and then the date that avoids penalties.
For arguement sake, let's use $800,000 sales price, and because you purchased the property 15 years ago, and I am keeping this very, very simple, your depreciated cost basis of the property is just $200,000. That is a $600,000 capital gains, which will be taxed @ 23.8% federal and let's thrown in 10% (whether that be WA or CA) for state income tax,,,,, that brings the tax into the $200,000 range!
the risk of penalties and interest if this isn't done correctly could exceed the cost of hiring a tax accountant. Best to figure it out by June 15!
