In Florida it is 3 years. The interest rate is what you bid on with the low bidder winning. If you have a desireable piece of property like in no mortgage and good resaleability, you will have competition and will get a lower yield. Still usually 10% or more. If the taxes go unpaid for 3 years, the property becomes yours subject to outstanding debt. It is imperative that you do your homework first and know that there are no outstanding filed public liens ahead of you in excess of the value of the property. After you have bought the cert, the owner can not take any new loans on the property without paying you your money first.