Dread Banner Quality

I'm wondering if I'm calculating this right.

DB gives .5% effect of aura per quality and 20% impale effect at lvl21 so with a lvl4 enhance and 21/23 DB you get 47% quality

I assume;
.5 * 47 = 23.5%
20 * 1.235 = 24.7% effect of impale

Math is hard, am I doing this right?

Sounds about right, yes.

Close, but you cannot calculate that last .5% from quality. It will always round down. I’m pretty sure impale effect will also always round down. So you get

.5 * 47 = 23.5 = rounds to 23%
.20 * 1.23 = .246 = rounds to 24% increased impale effect

Obviously DB quality will stack additively with any increased effect of non-curse auras you have. You also get aura bonus for the chance to impale and less accuracy.