Calculating RMD

Calculating RMD.  I turned 72 last year and trying to determine my rmd.  My wife has a retirement account and so do I.   She will not turn 72 till next year.  Given that, is my RMD calculated only on my account?   Or both of ours.  Secondly, I assume that the RMD that is required to be pulled is before taxes on this withdrawal.   Example, if my RMD was $50,000 do I just have to pull $50,000 or have to pull $50,000 plus amount to cover the income taxes?