if you are in the 20% qualified div bracket then you are probably also in the zone for the Net Investment Income Tax of 3.8% which would give you 23.8%. whenever you add more income there could other effects on your 1040 such as deductions phasing out and also penalties in the amount due to the Fed if you are just looking at the running total on the desktop version, so you need to look at effect on your 1040 as a whole line by line.
