Banishing Stroke Miracle Converted Mana cost

[Swamp]

if I cast Banishing Stroke using the miracle ability, is its CMC 1 or 6?

[Jake1991]

Six.

Casting a spell for an alternate cost doesn't change it's converted mana cost.

[Arix]

Keep in mind that there are only two things that change a card's converted mana cost:
1. Copy effects. If you Clone a creature with CMC 6, the Clone's CMC will be 6 as long as it's a copy of that creature.
2. X. If you cast Blaze with X = 5, then while that Blaze is on the stack, its CMC will be 6.